Having to pressurise CH system on a regular basis

16 Dec 2008
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United Kingdom
Can anybody tell me why my CH system needs pressurising on a regular basis? I can set the pressure to 1.5 bar one day and it will have dropped to either 0.5 or even zero the next day. All my radiators are equally hot from top to bottom but when the heating has been on for about two hours the pipes start to 'click'. I am pretty sure the noise is upstairs somewhere and the boiler (Worcester 28 CDi) is in the loft. The boiler was fitted in 1999. I have checked for leaks at the boiler, radiators and pipework around the house and haven't found anything although some of the pipework is under my loft floor, which I installed many years ago, so I may have to lift the flooring to examine the pipes for leaks there. I put Fernox (is that the correct name?) into the system about three years ago. Any advice will be gratefully received.
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Check the 15mm copper pipe that goes outside. Fill up and watch the pressure guage on the boiler, does it rise above 3 bar (ish). If they are both ok i would guess its under the floor somewhere, if you can't see any damp patches its probably downstairs under the flooring. Failing these it could be your hex but this is not really a diy job.
Hi gigz! Thanks for your reply. I did have problems many years ago with high boiler pressure resulting in the relief pressure valve opening and water did come out through the 15mm pipe outside. At the time the pressure rose to 3+ bar and water was coming out of the pipe outside, so I had the relief valve replaced as I was told it was either faulty or not closing due to dirt inside the valve. All the pipework for the downstairs radiators is above the skirting boards and there are some pipes in the hallway that run upstairs. I assume they go to the boiler through the small front bedroom radiator to the airing cupboard where the pipes run up to the boiler in the loft. The upstairs radiator pipework is under the floorboards except for one that is in the front master bedroom. This was fitted as an extra one with its own pipework which is in the airing cupboard, because for some reason there wasn't one in that bedroom when we moved into the house. Another small radiator had been fitted back to back with the bathroom radiator by my brother - in - law who is gas - free certificated, but he has since moved back to Manchester from Plymouth where I live. The boiler has had a new gas valve, water to water exchanger and filling loop since 1999 when British Gas first installed it. I hope I have given you enough information for any further advice you may be able to offer me! BTW, the only other run of pipework to the two downstairs radiators in my living room and dining room, is behind the chimney breast, but this has been bricked up and plastered over when I had a back boiler and its associated pipework removed around 4 years ago. I don't think there would be a leak there but you never know! Hope I don't have to knock into that area! Lol!
Check the 15mm copper pipe that goes outside. Fill up and watch the pressure guage on the boiler, does it rise above 3 bar (ish).

Have you had a look at the pipe outside, as per Gigz's suggestion? Tie a plastic bag over the end of it to see if it collects water.
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Check item 15 FAQ this section, sounds like pressure vessel needs recharging.

Thanks! I will check it soon. I have tried to access the schraeder valve on the expansion vessel but there is no room and would probably need other items removing first. Even with the left side panel, front panel and lower control panel out of the way I still cannot access the valve as part of the filling loop assembly is directly underneath it.
Check the 15mm copper pipe that goes outside. Fill up and watch the pressure guage on the boiler, does it rise above 3 bar (ish).

Have you had a look at the pipe outside, as per Gigz's suggestion? Tie a plastic bag over the end of it to see if it collects water.

Hi, Yes I have checked the pipe outside and it is bone dry. As I mentioned earlier I had a problem many years ago with water coming out of the outside pipe, which meant I had to have the pressure relief valve replaced. A friend of mine has recommended a good local plumber who is going to come to check the system next week and see if he can solve the problem. Seeing as the boiler is now 15 years old it might be a good idea to replace it with a new condensing type, that is if he can work out whether or not I have any leaking pipework! Cheers!
As posted by others it does sound as if there may be a problem with your pressure vessel (PV), but you can only recharge the water side so many times before the PRV starts to run. Suspect that either the valve or diaphragm may be a problem in the PV. Just recharging the PV is unlikely to solve the problem.
First of all confession time! I managed to reach the PV air valve and let a tiny bit of air out and saw no water. I then (mistakenly!) tried to put my pencil type tyre pressure gauge on the valve to see what pressure was in the PV. You've got it! I let some more air out! Lol! Anyway, when I ran the heating the pressure gauge reached 3 bar and water was dripping out of the pipe in the driveway, so I reduced the pressure using the PRV down to 0.5 bar, switched the heating on via the digital room stat and the boiler fired up. The pressure then rose to just under 2 bar and remained there. After a while the boiler tripped out and then back on again after 3 minutes. It did this continually and all the radiators are hot, so I'm not sure if all is well or not. I also noticed that when the digital room stat had reached the 20 degrees I had set it at that the boiler went out and only came back on when the temperature in the room dropped below 20 degrees. Is all well or is the boiler tripping out and back on again after 3 minutes a fault! Hope to get some feedback soon. I'll tell my friend's plumber mate all of this when he comes next week. Thanks to everyone who gave me advice on this post!

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