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Boiler losing pressure

Postby jrterror » Tue Nov 16, 2010 3:51 pm

Hello everyone.
May I say from the start, thanks for reading this. Yes you!
Right, on with the show. I am having problems with our ARISTON Combi A 24 MFFI boiler. It has been losing pressure and cutting out. I have located a leak on one of the radiators and intend to replace it. However I did isolate the radiator, thinking that this was the cause of the pressure drop. Well at least I thought I did! I got up the next morning after turning off the valves to the offending rad the night previous, only to find that we had no heating and no hot water. One side of the rad has a TRV fitted. I assumed that when turned to the off position that this would turn the valve all the way down, totally cutting off water into the rad. Is this correct? Do these TRVs not always fully stop water flow? I thought that this action would stop the system losing pressure and cutting out, but apparently not.

This morning at 0700 I decided to experiment, much to my wifes disgust I switched off the central heating. I repressurized the boiler to the Ariston recommended pressure of 1.5 bar and endeavored to monitor the situation, not easy because the boiler is in our loft space. Approximately 8 hours later, with the heating off it has lost only around 0.25 bar. I did notice earlier though, that when my wife went in the shower that the pressure did drop around 0.25 bar when she turned on the shower. When she turned off the shower it increased to near enough the 1.5 that it started at.

I perhaps should add that yesterday after repressurizing the system I returned home to find the floor outside wet underneath the boilers overflow. I can only assume that this is some kind of pressure relief tube, it is made of copper. (I do not believe that it is the boilers condensate discharge because the installation requirements in the manual indicate that this should run into a plastic pipe). Like today, I increased the pressure to 1.5 bar, but on that occasion did not switch off the central heating. As mentioned I returned home to see the floor wet, so obviously water had been flowing from it. We left the heating on for the remainder of that night, however when we got up this morning the boiler had cut out, with an error reading E02, meaning 'Pump Protect'. This is the confusing part, If the system is losing pressure, why did the pressure relief valve open?
I'm really confused.
Any help would be much appreciated
Thanks DG
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Simply Build It

Postby plumbbob » Wed Nov 17, 2010 12:02 pm

Firstly to answer the question about the TRV. The answer is no for two reasons. Older TRV's can only be turned down to a "*" setting which effectively means the valve is in frost mode and will still open in the event of cold weather. Only valves with a "0" setting will close entirely. Also, radiator valves are not guaranteed to be 100% watertight so it is not unusual to see valves weep even when fully turned off.

Looking at the system pressure on a minute by minute basis is unlikely to tell you anything. As the water in the system heats and cools it will expand and contract so the pressure will rise and fall naturally.

Maybe you inadvertently discovered the fault by seeing the wet patch under the pressure relief valve. This should always be dry. Possibly it is leaking or the pressure in the system is rising for some reason causing the valve to open.
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Postby Cheesie1 » Wed Nov 17, 2010 4:13 pm

The pressure relief valve can pass even if the pressure hasn't hit 3bar plus. If u find water dripping from ur pressure relief pipe (the copper one outside) it's probably just got muck on the seating, u can remove it and clean it if that doesn't work just replace the whole PRV, this will solve the issue of u losing pressure.
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