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Dear All Hello I am new here and have been reading all your posts with great interest. I found this forum by accident trying to find out info about the problem we are having with our log boiler. There are 2 problem which are happening, we have 45kw boiler and 2200lt buffer tank. We cannot get it up to 45kw and at full burn it is only doing 32KW, the flue gas is over 200 degrees. Our plumber and the distributor have checked it and it is burning fine etc and the wood is well seasoned but for love nor money we cannot get any more wattage out of it. The next problem is after a burn has finished it only heats unaided for a max of 1.5 hours before the buffer tank de-statisfies and the temp at the top and the bottom are in the 50s. As soon as we put on a rad circuit it crashes and the oil back up boiler comes on. I have done loads of tests and at its worst the top of the buffer went from 82 to 67 degrees in 15 minutes. We do not live in a sauna and we don't use all the rad circuits on extensively at all. We have 2 rad circuits one for our bedrooms with is on from 6 to 10 in the morning and then 4 to 10 in the evening. We have the office rad circuit and this runs for 1 hour in the morning and 2 in the afternoon. The guest area circuit is off most of the time. We have about 110m2 of underfloor heating and this is on during the day 19 and at night 10 so it is practically off. The DHW is on all day from 5.30 to 10 at night. We have had the boiler since the summer and have really only noticed the problems in the cold weather and we are now into our 4 th week of problems, as soon as the circuits come on it crashes and the oil boiler comes on.The tank has been charged at night so that the top of the tank is in the 80s and it stays like that all night but then the water mixes in the morning so all the radiators go off after 1 hour max and there is no hot water.
We have spoken to somebody who have the same set up and it works fine for them and they only do one burn a day and get 18 hours out of the buffer tank, they have a similar sized house but don't have under floor. They have their rads on flat out and see no difference in the top temp of the buffer it just carries on quite happily.
We were told by the distribtor that we could only ever get 2 hours out of the buffer of unaided heating before we would have to relight the boiler and burn again. Some days when it has been cold we have burnt all day and then by the morning when the circuits come on it crashed. It can happening in the evening too after burning all morning and early afternoon. If we had known from the start we would only get 2 hours of unaided hear we would never have bought it and gone for a boiler stove instead, we might have got more hot water lasting for longer etc. Not sure what to do and just thought there might be somebody on here who has had a similar problem. I am not sure if I am allowed to mention the make of the boiler on here but it was expensive and came from Austria. I have attached one of the tests I did showing a burning cycle over a period of a day and you can see what is happening and when the oild boiler comes on. Thank you in advance for reading this and really look forward to your comments Thanks again Tcgaisford
A few questions Charlotte: 1.) What pipework controls do you have on the CH circuit, e.g. do you heve something like an Acaso automix linking the flow and return. 2.) Do you have a " smart"modulating pump. 3.) Do all your rads have TRVs 4.) Is your CH pipework all well insulated. 5.) How do you supply your DHW. 6.) Do you charge the store up to 85°top to bottom.
With respect to boiler output, what is well seasoned wood - one year dried under cover, 2 years ditto or more? Is the wood seasoned cut and split or in log form? Have you moisture tested it? What size are you burning, I have found that large pieces do not produce the output (but last longer in the boiler) I try to avoid putting larger than 10-12cm in the boiler if I want a hot burn and split somehow seems better than round wood. I have come to the conclusion that the output is down to the available surface area that can burn at one time. Peter
The figures you give for the depletion of the tank imply a load as high as 76kW (half the tank falling 15C in 15 mins) which seems unlikely so the tank probably doesn't have as much energy in it as the temperatures might suggest?
Owlman Thanks for your questions I will try to answer them below
<blockquote><cite>Posted By: owlman</cite>A few questions Charlotte: 1.) What pipework controls do you have on the CH circuit, e.g. do you heve something like an Acaso automix linking the flow and return. We have pumps next to each other with the cold and hot return going through them we can regulate the speed of these pums, I am not sure what an Acaso automix is would it be with the pumps. I know we have some sort of mixer because it mixes down the rad water from the top of the tank and then underfloor coming back in. 2.) Do you have a " smart"modulating pump. Not sure what this is, is it at the back of the boiler? where do I need to look for this one and what does it do? 3.) Do all your rads have TRVs Yes we have thermostats on all rads and controls in the house. 4.) Is your CH pipework all well insulated. I think so, most of it is under the ground with grey insulation and filled in with screed or concrete. Some of it is under the underfloor with kngspan. We did find some in a roof space which wasn't insulated and we have just had that done. What would you say is good insulation? 5.) How do you supply your DHW. We have a hot water boiler the buffer tank tops this up and the boiler controls the temp of this, we have not had problems with the DHW as with the radiators. The boiler is always keeping this as constant as possible through the day at 65 6.) Do you charge the store up to 85°top to bottom.</blockquote> It would be a miracle if we charged top and bottom to 85, I have just been out tonight and it is 85,78 and 68 and the burn started at 4 and is nearly finished and it is now 10pm. We burnt this morning from 8.30 to about 1pm today aswell. Thanks for you help Charlotte
Hi Peter We have to use 1/2 metre logs for the boiler and cannot use short ones, the wood has been seasoned for about a year and is light and quick burning at the moment, it has all been spit in half. We did use some hard wood before this softwood and we were still burning more than once a day just to get hot water with that and that was very well seasoned. Thanks Charlotte
<blockquote><cite>Posted By: CWatters</cite><span>How are you measuring<span id="dtx-highlighting-item" dtx-Highlight-BackgroundColor="lime">boiler</span>output power?</span>
The figures you give for the depletion of the tank imply a load as high as 76kW (half the tank falling 15C in 15 mins) which seems unlikely so the tank probably doesn't have as much energy in it as the temperatures might suggest?</blockquote>
I think you are right and I did all my logs taking readings at certain times. I used the computer screen on the boiler to get the buffers temps, flue gas, and boiler temp. I used the meter at the back to get the KW, hot and cold and lt/h readings. I have attached another test I did the next day so this might help too.
If any of you have any theories as to what is happening do please let me know. My plumber thinks it is because we can't get the output of the boiler. I think it is something to do with the flow and return temps ruining the buffer tank temps and spiking into the hot water at the top and bringing cold water up and then it all mixes. I will try and attach second test to this message Thanks again Charlotte
Hi Charlotte When I mentioned wood size of 10 - 12 cm I was talking of diameter not length. It is correct to put in 50cm long lengths (I presume the boiler fire box is about 55cm long) The calorific value of wood is dependent on weight, the amount of energy / kg is almost the same between soft and hard wood, just that for a given size the heavier hard wood will have more energy, roughly speaking. One years seasoning is not much, 2 is better, I use 2 year wood some here will recommend 3 years seasoning. Being light for its size does not guarantee dryness, just guarantees not many calories. Was the wood split and cut to length a year ago or was it seasoned in the log? Unseasoned or poorly seasoned wood will significantly reduce the energy available to do useful heating. It is a common problem of getting good quality firewood and the amount storage that proper seasoning requires.
A diagram of the boiler / store / heating connections with the pumps and valves labelled by type would be useful!
To me it sounds like the low output from the boiler and the destratifying of the store are 2 separate issues. The output at 32kw is just below 1:70 with the TS which is within the recommended ranges given by various manufactures which are typically between 1:50 and 1:75, so I would expect the system to work even at the reduced boiler output of 32kw.
I get very nervous about insulated underground pipes - difficult to see problems. With the heating running can you measure the temperature of the pipes at the boiler site before it goes underground and then measure the temperature at the house where the pipes emerge from the ground to help determine if there is any / much heat loss along the pipe run. Peter
Have you tried running some tests with different ages and types of wood. Have you invested in a moisture meter for the logs? I burn oak, at least 2 yrs old, I have been told to mix it with other woods, but it doesnt seem to need it with simple log burner. Keep us updated please!
Firstly I am a supplier but i would just point out a couple of things; 1. Fuel Quality is essential for output from the boiler. Split your wood and test with moisture meter on the inside face. You are looking for 15 to 20% moisture content for the very best output. You need to know this to be in total control. This will require wood to be seasoned typically around 18 to 24 months. 2. Ensure you are as fully insulated as you can be...not only on the house but also on the installation (Pipework and accumulator tank). 3. As you say there should be a 3 way valve on the flow from the buffer tank. You have to serve 3 masters [1] cylinder tank [2] radiators [3] UFH If there is large heat loss from the buffer tank it is a good idea to fit a Thermomatic K to motorise the 3 way valve to maintain a constant flow temperature. Speak to your supplier/installer about this. Set a constant flow temperature of 60°C and this should help ultilise the energy in the tank and maintain heat stratification. You need to also try to control the temperature to the manifolds on the UFH as these typically will want 35 to 45°C. The design of the heating circuit is critical in obtaining the most from the energy stored from the buffer tank. Lastly some pictures of the Installation would help people to give comments along with a schematic diagram. If the worst comes to the worst the boiler manufacturer should have a top MCS accredited installer with good experience who for a charge could come and check all aspects of your installation i suspect.
Hi Again and thanks for all your comments. I have to admit that maybe the wood could be not as dry as it should but the plumber who installed the system and the supplier/commissioner have said that the wood is OK and it is getting a good flue temperature and clean burn. Every time we change fuel we have to callerbrate the boiler again when it is in full burn by the installer. I will investigate this more though and thanks for the advice. We have quite a bit of wood and also wood stored for later use drying at the moment. When we knew were were going to get this boiler we got quite a bit of wood ready. Insullation is out of my hands but I do know all the pipes have been insulated but how well I do not know. The buffer tank has a massive jacket around it top and bottom aswell. All pipes in boiler room are insulated. We have been trying to tell plumber etc about the Thermomatic K and they are just not listening they are just concentrating on getting the boiler output up. But I just know it is a flow problem too! I will try again and see what happens.
Hi I think you are right about the manifolds and I will post some photos and diagram, I just need to go into the office because they are on another computer. The suppliers in the UK are MCS accredited and they are the only supplier of this boiler in the UK. I did some tests this morning and this is what happened, I hope I haven't made it too complicated.
I woke up at 6 am and looked at the buffer tank before anything came on the tank from top tp bottom was 84/73/67, last night at about 10pm the bottom was at 81 At 6.06 the DHW came on it took quite a long time for the pump to come on for the DHW At 6.30 the readings were as follows Tank 82/72/66 boiler 74 and DHW still at 50 At 6.30 circuit 2 came At 6.36 the readings of tank were 84/68/58 DHW was 53, H return was 66 and cold return 52 At 6.40 the DHW started to rise it got up to 65 by 7.07 so took about an hour to reach this temp. While circuit 2 was running the temperatures remained quite constant including the h and c return temps. At 7.07 the readings were, tank 84/60/58 DHW 65 H return 66 and cold retrun 50 At 7.10 I put on another circuit (circuit 3). At 7.22 these were the reading after this circuit had been on for 10 minutes tank 82/58/48 DHW 63 hot return 64 and cold 49 From 7.30 the top tank temp started to drop and this was down to 72 by 7.55 the middle tank temp was 53 and the bottom 52 the boiler temp was down to 62 and the hot return was 62 and the cold 61 This test was done with DHW first running for 25 minutes before circuit 2 came on. Circuit 2 was running for 40 minutes before circuit 3 came on. At 7.55 I started to light the boiler again. I had to go shopping and I came back at 9.30 At 9.30 the boiler had been burning for 1.5 hours and these were the readings tank 77/54/54 boiler temp 84 DHW 55 Hot return 81 and cold return 61 the boiler was producing 29kw and litres per hour going around the system was 1300, the flue gas was 206. At 9.30 we have only 1 rad circuit going, the under floor and the DHW. I hope these figures are of help to you. The question I have is what temperatures are we trying to achieve after a burn and if left all night what lose do we expect from the tank. Also are the h and c return temps OK. Look forward to hearing from you and thanks again for your help Charlotte
I am in the office now so attaching docs, I am appling for RHI at the moment so have photos and diagram etc so will attach them to a few positings Thanks again Charlotte
Posted By: Tcgaisford................................It would be a miracle if we charged top and bottom to 85, I have just been out tonight and it is 85,78 and 68 and the burn started at 4 and is nearly finished and it is now 10pm. We burnt this morning from 8.30 to about 1pm today aswell.
Burning once a day in winter is usually the norm. I find that I can have about a 5 hour burn late afternoon into the evening and this supplies the evening CH, DHW and sufficient to last to the next morning's needs. I have a fairly large open plan bungalow that is a a bit leaky, so not ideal.
You have a good boiler, but as others have indicated, and your calculations support, the long burns seem to suggest thats it's not working at full efficiency, and probably due to fuel quality. The post burn store temperatures seem to indicate the store is loading, and stratifying OK. Maybe a bit more info about the wood, from you here.
The rapid depletion of the store could have several causes, the obvious overheating of the house which you say isn't the cause, or your house is even more leaky than mine, or perhaps the controls feeding the various heating circuits are not quite up to the task, and are simply either on full, or off. This, along with house insulation, and the fuel issue are where I would initially look.
You say the house rads are on for 10hrs daily, the office is on for 3 hours daily, and the underfloor on 24/7. That seems a fairly big demand. Is your house well insulated. System layout would be helpful but ultimately as winterbourne suggests it's the installers/designers who need to be contacted, and should still be under warranty. I'm a bit confused by your OP, you say you were told you would only get 2 hrs unaided CH, and then again you say if you'd known you would only get 2 hrs you wouldn't have installed it. Or have I got it wrong.
Looking at your schematic Charlotte It seems the flow to the CH circuits is coming off the primary store charging circuit as opposed to coming from the store. This may be deliberate, in order to prioritise the hot water to CH, as opposed to charging the store, it just seems a bit strange to me. It may explain why to some extent you can't ever seem to get a good charge in the store. Its because the boiler is constantly feeding the CH circuit and is lowering it's efficiency to cope with that "lesser" demand. If it were charging the store it could run at full blast unhindered. It may also point to the fact that your house insulation is not quite up to scratch. This sort of CH prioritised design may be fine for heavily insulated properties where after an hour or so of CH, the priorities switch and a good store charge takes place.
Hi Thanks for getting back to me so quickly, We are on a one level aswell and the house is about 5 bed with large open plan barn in the middle which is insulated to death! the cottage end could be a bit leaky and the office is well insulated. I have to say we didn't get on very well with the OP and he was only here for 3/4 hours on Tuesday and couldn't wait to leave. We did show him our tests and tried to tell him the problem but he just did not want to know, all very frustrating. I think he said 2 hours because he couldn't sort out the problem. He took a log of the burn he did to send to the manufacturers. He was blaming the meter at the back of the boiler and the manufacturers would be able to tell by the log figures from the boiler what it's output was really doing. We are still waiting to here back from him but no news yet. I spoke to my plumber and if it isn't putting out the correct output then he would campaign for another boiler. But I still think it is the flow issue and what happens to the heat loss from the buffer tank that is what is annoying us the most. I do understand about the wood issues and do some investigations. Not sure what do if the MCS man from the suppliers who commissioned it comes up with nothing. I know he is not a plumber and only knows about the boilers so he might not know about the plumbing bit etc.. What we really need is someone who knows the whole system. Do you think there might be someone out there? if there is let me know. I can't believe how helpful and kind people have been on this forum, I really appreciate it all. I can't tell you how stressful and frustrating the last 4 weeks have been. Thanks again Charlotte
Dear Owlman the boiler is still burning and the is up to 84 at the top but bottom still in the 50s. I have put the hot water on timer so it isn't on all day and I will see if that makes a difference. What you say about the flow being in the wrong place makes sense. We don't live in a sauna but it is cold up here in Northumberland but it is very mild at the moment. By watching the boiler it is always trying to charge up the hot water and it is keeping it up all the time and we aren't using it all day so it might help to just put it on when we need it, mainly in the evening. We also have a pump which produces hot water instantly when you switch on a tap and this was on 24 hours a day but we have put this on timer too a few weeks ago. Thanks again Charlotte
Dear Owlman just checked the output of boiler and it read 37kw which is the best I have ever seen, I will keep looking and let you know how I get on. I have stopped it charging the hot water unitl this afternoon. Thanks again Charlotte
Now that I've looked at the diagram I see the middle temperature sensors on the tank is well below half way down so the numbers I calcilated will be out. The store will contain more energy.
Here's an idea, so as not to inconvenience you, and If you already have a tank full of DHW. Then switch off the pump and isolate that particular circuit, whilst the boiler is running. That would mean that the boiler would only be supplying three functions instead of the current four. By eliminating the circuits one at a time like that and leaving just the store primary open you may get a better understanding and hence a steer in the right direction. What do you think CW? My system is quite simple compared to yours. I worked on the principle that the store is the heart of the system and everything feeds into, or out of that. The boiler is just the device that charges it. Then, who am I to disagree with messers Fröhling.
P.S. Do your boiler efficiency calcs with the boiler on and with just the store primary circuit open and running. i.e. CH and DHW off.
Hi I have switched off the DHW about 40 mins ago and the boiler temp is at 90 and the top of tank is 87, middle 84 and bottom 84 it is now at slumber mode. I know the man who came on Tuesday switched everything off and it took him 3 hours to get to the above temps but when the circuits came on it went down again. I will watch at 16.00 when things start to come on. At the moment we only have underfloor on at 19 degrees. Maybe it is plumbed in wrong, and the plans from the manufacturer is for new build european houses and not old farm buidlings in Northumberland which are not all as well insulated. like Owlman says and we should not have it on DHW priority and take the CH directly from the store instead. I will give you an update on how it is going this evening.
I'm thinking out loud here Charlotte but looking ot the schematic again, the return from the 3 circuits is fed directly into the store boiler return. Now, that return water could be fairly warm depending on CH and DHW demand. By pushing this warm water into the return pipe just before the loading valve, the boiler is probably sensing that the store is charged and starts to "slow down". It seems a fairly sophisticated machine. The upshot of this layout is that the boiler "slows" and the store never gets charged because the primary circuit is constantly being "hi-jacked" by the 3 pumped circuits.
Hi Owlman I really do agree with you because it has always felt that the temps coming back into the buffer seem to muck it up and I have always stood by that. The boiler might not be going on all power but it does charge the tank well when everything is off. I will have to talk to our plumber and I think I will have to leave it until after Christmas now because it is quite near and he had been going through this with us aswell. I think he is coming over during next week but I will email him today with your suggestions and tell him I have been on this forum. Thanks again keep think outloud!!! Charlotte
If it does turn out that the system layout is the fundamental source of the problem, it shouldn't be too onerous to adjust, assuming that there are sufficient unused store tappings available.
Hi Owlman I am so excited because all the tank it totally charged 89 top 89 middle and 85 bottom, the boiler is showing 91. The heating circuits have come on in the house although they are not set to come on until 16.00 this afternoon. I am sure there will be more tappings on the buffer tank because you can see the extra holes on the insulation. How would you change it? I will let you know how we get on tonight when the circuits come on. Charlotte
You don't want to be pushing the store up to a lot more than the present temps, otherwise the Pressure relief valves will probably "crack open" so if you've got all the pumps to your three circuits off, whilst conducting the experiment now's the time to switch them back on and so re-direct any latent heat still in the boiler. This manual exercise may get you through the holidays and allow you to achieve a full store charge untill you can have a proper look.
Hi Owlman The boiler did go a bit mad this afternoon and all the rads came on even though the timers were set to off, even on the room controls. The dhw was not on but the water temp was up to 61. The heating circuits have now cine on properly and the top is 89 mid 87 and bottom has gone down to 64 but this is also the cold return temp at the moment. I am not sure if it was doIng the Leginere thing that it is meant to do once a week where it pushes a lot of heat through the system. I did look at the kw and at one pint it said 65 kw. I think we will leave it for tonight and see what happens. It did help turning off the water because I really feel had charged up as much as possible. we are going out tonight but hopefully back early so will check then. I have emailed my plumber but have not heard so might not hear his comments until after Christmas. How long have you had yoUr boiler? Would love to know what temps you get your buffer tank and how long you wait between each burn. Thanks again Charlotte
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