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Boiler & System Pressure Problem
I have a 10 year old Valiant Eco Max 646 Wall Hung Sealed fan assisted boiler. It uses an external pressure vessel as it does not have an internal one. I have 30 radiators in my house, total output 42KW 470 litres. The pressure vessel capacity is 18 litres. We moved here 5 years ago. About a year ago I noticed I was having to top up the boiler from the cold feed fairly regularly in the mornings ( about every 10 days). (After the 10 days, during the night when everything was cold the boiler pressure dropped to zero on the boiler display and I then had to re-fill to 1 Bar.) However, after filling to 1Bar cold pressure once the boiler was up to temperature ( 65c ) that pushed the boiler pressure over the red 3 Bar limit and it vented outside. I thought that I maybe had a leak somewhere in the system. No signs of a leak anywhere even though we have concrete floors. After many weeks of fiddling, I discovered that if I set the standing pressure ( no heat) of the boiler to 0.25Bar and the max boiler temp to 60c the system worked within the boiler pressure guidelines and did not lose water. It did not drop the pressure overnight and only needed a minor top up every couple of months which I think proved I did not have a leak. However, I knew this was not ideal and reckoned the problem was the pressure vessel. So I got a local installer to review my problem. He agreed and a few weeks ago he change the pressure vessel. He said the old one had water on both sides of the diaphragm & so was clearly broken. However, the same problem has returned and I now have to top the boiler to 0.25bar max cold and set a max operating temp for the radiators of 60 DegC . This works ok just, but in very cold weather I would prefer to run the boiler at a higher temp. The installer says he can't help me further. I have bled all the radiators regularly, checked the capacity of both the boiler and the P Vessel for my system, and they are both ok. I would be grateful for any thoughts or ideas from your experiences. I am not an installer but I worked for a radiator company for 35 years so have a good working knowledge.