I too have a Worcester Bosch HE40 Plus Combi Boiler. For the last 3 months it has been constantly losing pressure and I have had to fill it up using the filling loop. Various plumbers have been called to see it and up until now they have all reckoned it was a 'microleak' in my heating pipes or radiators. I looked under the ground floor and at the ceilings looking for signs of a leak, but could find nothing. I thought I would just have to wait until all the water I was topping the system up with showed itself somehow. One plumber advised me to inject some Fernox leak sealer into the system to seal the microleak. I did this and for a day or so it seemed to stem the need to top up the pressure. I thought I had cracked it, then it started losing pressure again. I thought that it might need a higher concentration of the leak sealer, as it had worked for a while, but after adding two more units to the system it was still as bad. I trawled the internet for answers, it does seem that alot of people have this problem but no-one has posted an answer. I checked the pressure in the expansion vessel, via the shrader valve, it was fine. I tied a polythene sandwich bag over the pressure relief valve outlet to see if the water was leaking through the relief valve, but it was bone dry. I came to the conclusion that the water must be leaking from inside the boiler, but how to prove it? A post on the internet gave me a clue. After topping up the pressur to 1.5 bar, I closed the flow and return valves insiside the boiler to the radiators, effectively isolating the boiler and the heating system, and left it overnight. When I looked at the pressure the next morning it had dropped to zero. When I opened the valves up again the pressure went up to 1.5 bar again exactly where I pressurised it to. I tried the same exercise again during the day and found the pressure dropped to zero within an hour. I called out the Worcester engineer as my boiler is still within the two year warranty period and was able to categorically say to him that it was the boiler that was at fault not my heating system. He immediately replaced the heating cell/ combustion chamber which he said must be leaking water into the combustion chamber which was why there was no sign of water elsewhere. He also noticed that where the condensate drain ended there was algae growing under the drip of the pipe. He said that as the pH of the condensate was acidic algae should not be growing under the drip, which was another little clue as to the cause of the problem. In fact the condensate drain should not constantly drip at all, it should release the 150ml of condensate that has built up and then not drip at all until the next 150ml of condensate is released. If there had been a leak in the secondary heat exchanger which heats the hot water for the taps the pressure on the pressure gauge would rise because water at a higher pressure from the mains would enter the heating system. The only other clue that I had was that I got an error code of EA which meant flame not detected, I gather that too much water may have leaked into the combustion chamber and the gas could not be lit.
All this goes to show that the unthinkable can and does happen. Who would think that the casing of the combustion chamber/heating cell could leak in a virtually new boiler.
I hope that my findings help someone else identify their problem of having to constantly top up the system yet finding no leaks in the heating set up.
Bob, June 2007
