Hi Dan,
Apologies for my previous terse reply, I was in a hurry. I've just done a firing, and when my 2000l system is at 84 C top to bottom the pressure is 1.35 bar, If I take it up another 10 degrees ( my limit ), I usually reads about 1.55/1.6 bar. In your situation I would:-
A. Check the pressure gauge, Is it one inserted on the main boiler/store flow or something on the boiler?
B. Check the PRV, if possible, the valve seat may be dirty. What sort of valve is it?

Mike

Hi Dan
I've not come acroos any specific guidance for ATMOS in the manual - check what your store/accumulator is rated for before you get a higher rated safety valve. Should be 6 bar on the quench circuit.

Hi Dan,
Julian's right, the starting point is the pressure rating of of the boiler and the store. Most of the German stores I researched, when I bought mine were rated at 3 bar with a maximum temperature of 95 degrees. Another thread on this forum says that some of the AKVATERM stores are only 1.5bar. My boiler is rated at 2 bar so I set my PRVs (2 in total) to "crack" at 1.8 bar. It sounds like you have a preset PRV, there are adjustable ones on the market.

Mike

Hi Folks,

I wonder if anyone can offer me advice. I am grateful for all the advice that you gave me in setting up my boiler a few weeks ago. Now that it is up and running, I am very happy with its operation. But i do have a few issues with my heating zones. I know its something that I should be consulting with my plumber about, but he has a family member who is quite ill at the moment so it may be a week or two before he gets back to me. So I wonder if there is anything that I can do myself to alleviate my issues.

Firstly, my system:

25kw atmos gasifying boiler with 1500l buffer tank - no problems with its operation.
6 meter head Grundfos pump exiting the tank and leading to a cabinet in my utility room where it is broken into 3 zones, upstairs, downstairs and hot water.

Upstairs and downstairs and downstairs heating has worked perfect for the last 8 weeks. We moved in to the house last week and got our final fix plumbing installed and the third zone of our heating system is now in operation. ie hot water. Since then, when it is in operation, sometimes the other zones won't work, but sometimes they will. Sometimes, even when the hot water zone has switched off, the other two heating zones will not work or only a few of the radiators will heat up. If the hot water zone has been switched off for a couple of hours, then the two heating zones will normally work.

Its a pain as we cannot be guaranteed heat when we want it. Is there any way that we balance the system?
When the circulation pump is running to the hot water zone, ie. heating the hot water cylinder, then you can hear the water flowing through it very loudly. But if it is heating one or both of the zones then the circulation pump is almost silent. The pipes going into the hot water cylinder are 1". The pipes in the heating system are 1/2" and 3/4". If I closed the isolator valve entering the hot water cylinder to half way, would it help balance out the system a bit?

Confusing, I know. I'm sorry if it doesn't make enough sense, but I would be grateful if any could help me??

Dan

Hi have you got any check valves in to prevent back flow. You may have ended up with some pretty much dead water locked in a cicruit. It might not be obvious as it might only occur depending on which valve opened first, if the pump was already running when a zone valve opened. etc etc.
have you a grundfoss variable pump?
Try locking out each zone and running each individually and then work through each combination to see what happens.
Cheers
mike up north

Interesting Dan....glad you got it sorted out. I have a similar problem where the pressure goes from the system to the point where it won't circulate and I can't get to the bottom of it. At 80-85 degrees the pressure gets up to around 1.5 bar (1.5bar safety valve, 25kw Atmos, 2000L accumulator). When the water cools (to say 40 degrees) the pressure drops right off the guauge. Obviously the presssure would drop but in each case it drops too much. The system can be 'cool' i.e. around 40 degrees and showing nothing on the guauge. I top it up from the mains - to say 0.2 bar, bleed the air from the system, fire the boiler and it will all be fine...until it cools again at which point it will have lost pressure again. It looks to me like there must either be:
(a) a leak - in which case it ought to show up somewhere surely...as a damp patch or pool of water and there's no sign of either so I can't see this can be the problem, OR
(b) the safety valve may be releasing water from the system when I am not looking (have tried disconnecting from tundish and putting a bucket underneath to see if any liquid escapes but no sign of anything) OR
(c) something else....

The other thing is that the system isn't yet complete - some radiators are yet to be fitted and there are dead legs of pipe which may contain air. But even if I have an air/water mix to some extent shouldn't the pressure stay within a range? It still looks to me as though something has to be being lost from the system.

EDIT: One other question for ATMOS users: In recent cold spell the waste gas thermostat has not allowed the fan and laddomatt circulator to run - I have had to light the boiler and, once it is warm, the thermostat cuts in and pump and fan start. Initially I thought waste gas thermostat was faulty but now wonder if anyone else has had a similar experience? 2nd EDIT: It was a faulty waste gas thermostat, now replaced by ATMOS.

Hi Mike
Thanks. I have tried bleeding the dead legs but no real improvement. Pressure vessel could be the problem or indeed the PRVs. I have also changed some AAVs thinking they might allow air in at low pressures and found one had been badly fitted and had been leaking. But I still have the pressure drop. At 86 C (as high as it has been) the pressure varies between 1.4 and 1.6 bar. Anything below 40 c it drops off the scale. One issue might be insufficient expansion volume; there's the store at 2000L plus a lot of rads so maybe 200L vessel is too small? By my reckoning it should be enough. Haven't tried leak sealer - is that worth a try? That won't gum everything up will it?
Cheers
julian

Thanks Mike. There is just one PRV - not quality. I have tried putting a bucket under it but it didn't collect anything but I still have my suspicions. What you say about the expansion vessel sort of bears out my fear that, at a decent pressure when the system is cool, there may be insufficient room for expansion when the system is hot so the PRV lets some water go. There is more volume to add as well when the last rads are fitted. If that is the problem, could I fit another say, 100L vessel alongside the existing 200L rather than replacing it? And I understand the vessels are usually pre-charged with air. I know the heating engineer changed the pressure but what ought this be set at? Equivalent to the max system pressure i.e. 1.5bar?
Cheers
julian

Hi Mike
Happy New Year to you by the way. I have no paperwork for the pressure vessel - the HE took it off with him or chucked it. I will see if I can find something online.
I have just one pressure guauge about 5/6 the way up the accumulator with the PRV upstream of it on the same tapping branch. It did cross my mind that the guauge could be faulty - but it does seem to be reliably faulty if you know what I mean. Just talking to a friend who has had a vented system changed to pressurised recently and the engineer told him to expect air in the system for "ages" yet. So maybe this will settle down. It has been running since October and I have part drained down once or twice in that time so maybe it is simply the oxygenated water in the dead legs mixing in each time.
If your expansion vessel is set to the lowest system pressure then mine may be set too high. I will check it with a pressure guauge.
Cheers
Julian

Hi Mike
Thanks for that - by my reckoning the vessel volume is good enough so its either the pressure, or a fault with the vessel....or back to the leak theory.
Cheers
julian

With the freeze up of the drain (22mm copper from where tundish will be to external gully) and after reading about the frozen condensate drains elsewhere it struck me that 22mm copper running externally is always likely to freeze in this weather. Has anyone routed one into their internal drainage? This carries anything from the safety valve (likely to be >80 degrees c very infrequently) and the overheat protection valve - if boiler goes over 100 degrees c this lets in cold mains water to cool boiler and dumps it to the drain. I recall the heating engineer said "You want it going outside where you can see it" but, given that the pipe he put in has frozen solid these past days so neither valve could offer protection from over pressure or overheating respectively it seems like it would be a lot safer running it into a drain inside. The question is whether soil pipe could cope with near boiling water - albeit only a small volume?

Hi Mike,
Thanks for that - good thought. The "heating engineer" put the 15mm from the safety valve into the 22mm drain - so unlike a tundish the escape was invisible - until I substituted the bucket (his words were "Looks better than a tundish"....I think he meant "I forgot to pick up a tundish"). I will re route the drain inside to prevent the freezing up and, as you say, a tundish for the new safety valve and another for the quench valve. Not too worried about the plastic drainage - they must allow for hot water from washing machines etc and as you say it isn't going to be a lot.
Cheers,
julian

Julian,

I'm just wondering if you got your pressure drop situation sorted? I'm beginning to think that I may have the same problem myself. My 1500l buffer tank after a good burn is always low on pressure. When I fill it up with water to 0.5 bar and then light the boiler, the pressure gauge often goes to 1.5 bar and inevitably the prv lets water go out the drain. For example, if the whole tank is heated to 80 top and bottom, then when it cools, I can be sure that the pressure in the tank will be down at almost 0 again. I'm at the stage where I top it up once or twice a week now to 0.5 bar. I have a 220l expansion vessel, and going on Mike's figures above, it should be more than enough or could it be too big and be the cause of my problem?

Can anyone tell me what pressure should be in these expansion vessels? I have not measured it, but I'm guessing that If the pressure in the expansion vessel was over 1.5 bar, would this mean that the diaphragm would not expand when the hot water in the system expanded and that the expanding hot water would go through the PRV rather than expanding the diaphragm in the expansion vessel?? Its just a thought, even when the boiler is really hot and the water is pouring out the PRV, then the expansion vessel is never hot oe even warm.

Any advice appreciated!!

Some day it will work properly .... until then I'll keep searching for answers :)

Hi Dan
I'm sorry you're still having problems. I think I have the situation under control. I found a previously undetected leak from the safety valve - probably dirt on the valve seat as Mike suggested earlier. It's a slow but steady drip. At 80/80 degrees the pressure can be 1.5bar but then drops off a little more each day as the water cools. Once the water gets below 50 (as it does if I can't light the boiler for whatever reason) it's at 0bar and draws air in through the AAV's - I think. I have no expertise on these systems as you'll know but I don't think too much expansion vessel volume would give you any problems. I think it could be the pressure in the vessel and must check mine which came with a pre-charge -as I believe most do. Check your vessel during use as Mike suggests - mine works as he describes...hot around the inlet - cooler elsewhere.
I am going to drain a few litres from the store and fit a new safety valve at the top of the vessel (where Akvaterm suggest I think). Once that is working I will cap off the leaking valve which was fitted to a tapping midway up the store. As you say...one day it'll all work fine. Until then we keep searching!

Hi Dan
Glad you're getting there. What was the system pressure when you reset the vessel pressure to 1.2bar? Bening a maths (and physics) non-starter I'm not sure if I have understood Mike Up North's figures earlier. Is it as simple as the initial (cold) system pressure = air/gas pressure in expansion vessel?