Sealed CH system rapidly losing pressure,no evidence of leak

[Triafro1]

Hi,
I have a sealed combi boiler central heating system with a Potterton boiler, copper pipes and radiators on the first & ground floors of the house with the boiler on the first floor too. In the last 3 days a series of events / mistakes have occurred which have taught me a lot about central heating! Anyway, some constructive input would be appreciated, I'm not that keen on getting involved in the boiler or getting anywhere near the gas but if it is a problem with the pressurised water system then I would like to try and fix it without calling a plumber:

1. I put a screw through an upstairs floorboard and one of the CH pipes while the central heating was on. I turned everything off at the boiler including all of the inflow taps, mopped up a lot of water and repaired the pipe.

2. Once repaired I then turned everything back on including the filling loop which I left OPEN. So the system was pressurised at mains pressure. The next time the CH came on it worked fine (i.e. radiators got hot) but then I noticed that steam and hot water were coming out of the release valve outside the house. This made me realise that the system was under too much pressure and I realised the filling loop was in the open position so I shut it off.

3. Next time the CH came on the pilot light went out within a minute. I re-lit it and it went out within a minute again. I noticed that the pressure was practically zero in the system so I topped it up with the filling loop, then turned the filling loop off when the system got to around 1.5bar. The system then lost pressure over about 15 minutes back to nearly zero, it's currently sitting at about 0.25 or so. During this rapid pressure loss I checked the pipe I repaired and the external release valve, neither had any leaks or water coming out of them. I have not been able to detect any leaks elsewhere in the house. I also checked the bleed screws on all the radiators and none of them were loose or leaking, although I think the upstairs radiators (the boiler is upstairs too) have a lot of air in them.

Throughout all of this time the hot water has worked fine (if the pilot light is lit when you turn on a tap).

My next step was going to be to open up the filling loop at the same time as someone opens the bleeding screw on an upstairs radiator (which is now full of air, there's water in the downstairs ones). Then turn off the bleeding valve when the air is expelled (& water starts to come out) and keep the filling loop open until the system re-pressurises to around 1.4bar. Other than that I don't know - could a valve be letting air into the system from outside?

Thanks in advance

 

[Burnerman]

There's nothing wrong with your theories, its just that your system must be completely air free before you will get a steady and satisfactory pressure reading.
When the boiler is cold; pressurise the system up to 2 bar say, using the filling loop, and bleed all of the rads one at a time until the air has gone. Don't overpressurise - the PRV is notorious for letting water by once it has lifted.
Shut the filling loop completely off after every fill.
When all of the air has gone, pressurise up to 1 bar, and start the boiler. The pressure should rise a little. Check for air in the rads again, and top up the system as necessary. Disconnect the filling loop afterwards.
If the pressure gauge bounces around a bit, check the air pressure in the expansion vessel (usually about 10 psi with the system depressurised).
However.....due to the system having lost some of its water, your inhibitor level will be very much diluted and you'll need to address this - maybe by injecting some fresh stuff into a convenient radiator.
John

 

[T0YB0Y]

Hi , remove all air from your rads as you said and get pressure to 1 - 1.5 bar on boiler,Then without using your boiler for heating or hot water observe pressure to see if it still goes down if it does and you have no internal water leaks I would suspect the pressure relief valve has not seated properly after you over pressurised the system ( it may only drip very slow but this can easily be missed due to weather conditions). If this pipe is accessable tie a clear lunch back tightlty over it to see if water gathers. If the boiler only loses pressure when the the boiler is on then the pressure vessel might need charging with air, this would be noticable with the pressure climbing to 3 bar.