The expansion vessel would not stop the water from heating up, it is for allowing the water in the system to expand when the temperature rises without increasing the system pressure. There are 2 types of expansion vessel, one is for the boiler/radiator system and the other is if you have a unvented cylinder, some of which use external vessels, to allow for the hot water to expand. I would say it is more than likely the diverter valve, you may have either 2 x 2 port valves, one for heating and the other for hot water, or 1 x 3 port valve. It could also be that the cylinder stat is not working. Expansion vessels do go wrong, sometimes they need recharging by pumping them up, most times the diaphragm splits inside. They do not stop the water from heating.

I am not saying everyone is unhappy with the cover, if they were then no one would sign up for the product. What I am saying is that in over 25 years of doing this work, I would say that 8 out of 10 customers that I have come across have repeated the same story over and over, and that they are not happy. I have been paying for 10 years, I need a powerflush, cannot get the parts, 6 different engineers cannot fix it, I have been waiting weeks in the cold etc.etc blar blar blar. As regard the fact that a service is included, if you think sticking a probe in the flue and testing the co/co2 is a service the you are mistaken. A service should include, stripping the boiler, cleaning the heat exchanger, burners, checking ignition gaps, checking burner pressure, gas rate, checking safety devices, expansion vessel pressure , water pressure if sealed system, cleaning condensate trap, co/co2 etc. What British Gas do is a Safety Check not a service. But it is a free country and everyone has a choice.

No you are quite right I would not put a heat exchanger in for that price, more like £450.00. However if one of my customers had a problem like that I would advise that they replace the boiler and not waste their money, if it has got to that stage. It is all very well having pcbs, pumps changed for £200 per year, but if you add that up over 10 years it is £2000.00 or more and then their is a chance that they will not repair it due to sludge, so you will still have to pay for the repair on top. If you paid for each repair as it happens it would not come to that amount, one of my customers was being charged £400 per year for their British Gas cover because they had multiple claims, and then they said that they would not cover it unless they paid £800 for a powerflush , and then they said they need a new boiler. Sounds like a bargain ! I thank you.

This boiler is a room sealed boiler, the safety of this boiler will be compromised if there is a hole in the casing as the products of combustion will be able to escape into the room, which will have dangerous consequences. I have come across so many customers now who have been paying for this cover for years and years and then they have a problem like this and find that they have no come back to British Gas. When will consumers learn. British Gas has a clause, or should I say a few clauses to cover them, if the boiler is beyond economical repair then they are not responsible. If you have to many call outs from them. they will then say that the problem is due to Sludge and you need a Powerflush, which you have to pay for. At the end of the day they are a large business and are only interested in the bottom line, and that is profit, not the customer. Take my advice get another boiler fitted by a independent gas installer and if it goes wrong just pay for the repairs as and when required. You can try edited if you are in the Greater London Area.