Discuss Combi boiler - bang when hot water opened in the UK Plumbing Forum | Plumbing Advice area at PlumbersForums.net
By DCV you mean directional control valve (double check valve)? If yes, then I don't have it installed at all. I think it's the other person on this thread who has it installed. Also, by setting the air end pressure to 2.0 bar you mean setting it on that little expansion vessel?Can't say I agree with installing a DCV as a E.vessel/shock arrestor should allow water to move both ways. I would remove the DCV and also set the air end pressure to 2.0 bar
Thanks. I just had a look. That expansion vessel is precharged to 4 bars so if I am guessing correctly if the water needs to expand it needs to do it against the membrane that is pressurised to 4bars and this is effectively hard to do. When pressurised to 2bar it will be basically easier for the water to push that inside membrane. I hope my understanding is correct.Yes, on the expansion vessel.
Just noticed that its your boiler water pressure gauge thats jumping? re post 34 above, you need a tyre pressure gauge to stick on the air end schrader valve on the expansion vessel, you can then reduce the pressure to 2 bar by pressing the pin on the schrader valve to release some air until pressure gauge reads 2/2.2 bar.Hello, I am newbie in this forum. I had exactly the same boiler installed around November 2022. It was all fine for some time but then exactly the same issue started happening. I had the little shock arrestor added but that did not helped. I had Viessman checked the boiler and they said that basically everything is fine. They also replaced the little gauge.
I am really curious whether you managed to solve the problem? It clearly something is to do with the pressure and this only happens when I open any hot water tap. Similarly to yours I had open vented system converted to sealed one. I have also installed Aladdin auto vent valves to all radiators.
I also noticed that the pressure reading on the gauge is always higher by about 0.3 bar than on the electronic display but that might be just red herring due to where the electronic gauge actually measures the pressure.
Yes, it is. The other member has the same problem.Just noticed that its your boiler water pressure gauge thats jumping? re post 34 above, you need a tyre pressure gauge to stick on the air end schrader valve on the expansion vessel, you can then reduce the pressure to 2 bar by pressing the pin on the schrader valve to release some air until pressure gauge reads 2/2.2 bar.
It says Precharge: 4.0bar hence my thinking.4 bar seems very high how did you get this info ?
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