Condensing boiler pressure problems

10 Jan 2008
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United Kingdom
Help please. We had a new glowworm condensing boiler fitted (and the rads pressure cleaned) a couple of months ago and are having problems with the pressure. It was fine at first when we were just heating hot water and one of the radiators, but since opening all the radiator valves and using the central heating we are having to top up the water every day to keep the pressure up and keep it working.
The pressure is maintained better when the heating and water are on constant, but when it is off for any length of time it won't restart and we get an error message. the pressure is very erratic as well when it is on. We have checked everywhere we can and cannot find a leak; we have put a bag on the boiler overspill pipe and it is dry; we have had no water from any other overflow pipes and our hot water tank is just two years old.
Any ideas or previous experience of this problem greatly appreciated. The plumber who fitted the boiler is scratching his head (but hasn't looked at the system yet)
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generaly pressure problems in combi boiler signifies you have a leak somewhere, this leak could be that small that it has evaporated before hitting the floor showing no signs of a leak, if this is happening on a couple of radiators the pressure will go down fairly quickly. i'd go round checking every visable joint on pipework, radiators including the valves and do it a couple of times,rubbing your finger on the joints or a folded up tissue so you can see any damp patches if theres nothing visable it could be inside the boiler, but the water pressure must be going somewhere. combi's have a safety device on them that when theres no pressure or very little pressure the boiler will shut down to prevent itself from burning out. on the other hand the expansion vessel (which will be located inside the boiler) could have gone if this is the case when the boiler is on the pressuer will creep up and up and up to the point where it will blow all the pressuer out of the boiler out of the blow off which should be a 15mm copper pipe sitcking out of the wall outside and curled under so its practicallytouching the wall.
hope this is of some use to you
Pressurise the boiler up then turn off the ch flow & return isolaters under the boiler. Leave as long as possible.

If pressure doesn't drop, then it proves the leak is on the pipe work or rads.
recently had this problem on a boiler myself, turned off the flow and returns and found a leak at the boiler. took a good while to discover the secondary heat exchanger was leaking and draining through the condensate. just a heads up, might save you a bit of time! :D
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Thanks for taking the time to respond, I have found a plumber who will tackle the problem for me, he's going to check the boiler and the coil in the hot water tank for leaks, and go from there. Hopefully the concrete floor won't have to be dug up!
Just to finish the story. The boiler was checked and all OK, no leaks there. The plumber checked for leaks in the coil inside the hot water tank by emptying and looking in through the immersion heater hole, no leak. He then increased the pressure in the boiler to see if that would bring anything to the surface and we noticed a warm patch in the kitchen which we thought might be a leak, so he dug a hole in the floor and just found healthy dry pipes! We then found water under the carpet in the hall by the radiator, I never thought I'd be so glad to find a wet patch! He's coming back later to dig up the floor and fix it. :D
Is it generally the case that if you have a water leak from UFH in a concrete floor that you will find evidence of tbhis on the surface?
In plumbing/heating it is generally the case that every rule is proven by many exceptions. Water escaping from a system can come up anywhere, usually following sod's law.

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