Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




Heating and cooling: Pressure up and down on thermal store

Bottom of Page

1 to 14 of 14

  1.  
    • CommentAuthorjhsigma
    • CommentTimeFeb 17th 2020
     
    Hello need some help I have just had a thermal store installed with oil and wood burner feeding it, the problem is the pressure varies through the day from zero to 4 bar my installer says its air from the central heating system (which was a standard vented system been running fine for 6 years ) and as such nothing to do with him .I have been venting the pressure on the top of the store at least once a day and recharging with water since before xmas and its not improving ,is it a problem if I just leave it ? or any ideas , thanks John
    • CommentAuthorowlman
    • CommentTimeFeb 17th 2020 edited
     
    I'm guessing the CH ( you say is open vented), is totally separate from the Thermal Store apart from a coil within the store? If so then the CH cannot affect the Pressurised? store, i.e. they are not linked. Is this correct or have I got it wrong?
    •  
      CommentAuthordjh
    • CommentTimeFeb 17th 2020
     
    Posted By: jhsigmaHello need some help I have just had a thermal store installed with oil and wood burner feeding it, the problem is the pressure varies through the day from zero to 4 bar my installer says its air from the central heating system (which was a standard vented system been running fine for 6 years ) and as such nothing to do with him .I have been venting the pressure on the top of the store at least once a day and recharging with water since before xmas and its not improving ,is it a problem if I just leave it ? or any ideas , thanks John

    Hello and welcome. I think you're going to need to give us some more information. Specifically starting with whether the central heating is open-vented or not, whether the thermal store is open-vented or not. Then how are all the circuits connected to the thermal store, and what are those circuits? Are they open-vented or not etc etc. It might well be simplest to start with a diagram showing how it is all plumbed together. Brand/model names might help too.
    • CommentAuthortony
    • CommentTimeFeb 17th 2020
     
    There could a pin hole in the high pressure side

    I would collect some of the gas that you are venting in a small plastic large neck bottle , run outside and put a match to it, it could be hydrogen that forms as the system rusts from inside producing black iron oxide and hydrogen from iron and water
    • CommentAuthorjhsigma
    • CommentTimeFeb 17th 2020
     
    Thanks for your input ,this is a sealed system (the old one was vented ) both boilers feed into a n Advance Universal mutltifuel thermal store Everything works fine until the heating comes on (which was from the old vented system) but now joined to the sealed Advance store ,after the heating has been on for about half an hour the pressure starts dropping to zero I release some pressure (air?)from the vent at the top of the store recharge with cold water and everything is OK but this needs doing three times a day to keep the pressure in the range set by the installer (1to 2 bar )I have tried turning off all the radiators bar one but it makes no difference ,there appears to be air ingress from the heating side but cant establish were ,there are arv's on the flow and return but they dont seem to release the air ,there was never a drawing done of the installation apparently but could do a schematic ,hope this helps John
    • CommentAuthorowlman
    • CommentTimeFeb 17th 2020
     
    A few things to check:-

    Is there an Automatic Air Valve at the highest part of the CH system.

    Have you checked the Pressure Vessel. There should be a Schrader valve on it where you can do that. and repressurise if necessary. Sometimes the internal diaphragm bursts and water enters the air side creating many of the problems you're experiencing. Your installer should have checked that but just in case?

    Is there a Pressure Release Valve on the system with a tundish to outside, and is that leaking? Sometimes calcification causes them to remain open.
    • CommentAuthorjhsigma
    • CommentTimeFeb 17th 2020
     
    There is an arv about a metre from and higher than the gauge ,good idea to check the pressure vessel will do that ,there is a pressure release valve with tun dish and always get air out first will try lighting that to see if its hydrogen as suggested ,the installer has come on now saying we need to rip out bits of heating pipe to find the leak as putting pressure on the old system may have caused it to fail but as the pipes go under the floors and in the walls is going to be a mess is there any way of establishing which area the leak may (or may not)be without ripping the house apart .Thanks all for your input ,also still not clear why the arv's dont release the air John
    • CommentAuthorowlman
    • CommentTimeFeb 18th 2020
     
    If you check all the stuff I mentioned above and come to a blank which your installer may have already done then my inclination is to go with his assessment.
    If previously you had an open vented system then converting it to a pressurised one, may have put strain on a weak joint or two. Your action of using the filling loop each time you had a pressure drop may be pi...ing water out somewhere unseen.
    Before you go ripping out the whole or chunks of pipework you could try a gallon or so of leak sealer. De-pressurise the system and drain some water off and then top up with sealer, heat and circulate for a day or two. Obviously first check all visible pipework/ valves for signs of leakage.
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 18th 2020 edited
     
    If it were my system, I would ;

    -isolate the radiator system from the rest of the thermal store
    - add a pressure gauge, and a short circuit connecting the flow and return where it was connected to the thermal store (could be hose with jubilee clips).
    -pressurise the radiator circuit to 2 bar, and see if any press drop occurs.
    - if nothing happens, then switch on the circ pump
    - observe the pressure gauge again, likely very quick drop by your description

    This will at least confirm where to start looking, and you'll know it's not the NEW part installed by the plumber.

    I'm not clear why so much air comes into the system so quickly. I don't suppose there could be an issue with the rad circ pump, drawing air in on the suction side? You're suggesting that there is no problem until the radiator circuit starts running. If there were a simple leak in the rad circuit, it would depressurise, irrespective of the circ pump.
  10.  
    Is the expansion pressure vessel big enough for the volume of both the thermal store *and* the volume of the previously unpressurised radiators and heating pipework? How did the installer calculate this? Or did he think it wasn't his problem!

    If it is not big enough, or not correctly pre-charged, or the bladder has burst, then when the radiator water gets hot and expands, the pressure will rise and the pressure safety valve will dump some water. When the circuit cools, the pressure will fall very low as now there's not enough water. This will cause the dissolved nitrogen in the CH water to un-dissolve and collect into bubbles. Divers call this effect 'the bends'. Or, if the pressure falls to 0bar, air can be sucked in through the arvs.

    A leak will not cause the pressure to rise to 4 bar, as you mentioned, that kind of pressure can only come from thermal expansion. Safety valves are often set to open about 3.5bar.



    Can you access the pipe where the pressure safety valve discharges outside? Fix a balloon or plastic bag over the open end and see if it collects water.

    Don't ask how I know about this.....
    • CommentAuthorphiledge
    • CommentTimeFeb 18th 2020
     
    As Will says above. If the system is holding 4 bar when cold then a leak is highly unlikely unless its pump seals or MOV seals that leak only when they move.
    •  
      CommentAuthordjh
    • CommentTimeFeb 18th 2020
     
    Posted By: WillInAberdeenCan you access the pipe where the pressure safety valve discharges outside? Fix a balloon or plastic bag over the open end and see if it collects water.

    There's a tundish so it may be the overflow doesn't go outside. Ours goes into an internal soilpipe, for example.
    • CommentAuthorCWatters
    • CommentTimeFeb 18th 2020 edited
     
    Before ripping out any pipes....

    Common place for leaks are where pipes join rads. Feel around all the pipes and the floor/carpet with dry hands. Diverter and isolation valves are another problem area. Heck personally feel every bit of pipe you can reach.

    If it's now a sealed system there will be a PRV (over Pressure Relief Valve). These are prone to leaking once opened. You mentioned the pressure went upto 4bar. Most PRV open at 3bar so there is a good chance it's opened at least once and could now be leaking.

    If the expansion vessel is too small it won't stop the pressure rising when the system it heats up. So an undersize expansion vessel can force the PRV to open when the system heats up.


    If everything above checks out I would isolate sections of the old system and pressure test each section individually​. If necessary add isolation valves or even cut and cap pipes to allow this to be done.

    Edit: sorry if that's repeating advice already given.
  14.  
    There's a tundish so it may be the overflow doesn't go outside.Ours goes into an internal soilpipe, for example.
    Thats easy to reach then! Hose it into a bucket to see how much the prv is releasing.

1 to 14 of 14

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press