Ringoffive: I have no personal experience of working on a keston boiler so i did a bit of research. Google "heat exchanger gone in my keston c40 boiler" and do some research yourself. You "might" find it cheaper in the long run to have a new boiler fitted. Or if a member of your household is on certain benefits then you may qualify for a government grant....look up "warmfront" This could simply be a case of "balancing" your radiators. Without looking its hard to say. One thing i have noticed on new build houses is when the plumbers do the first fix pipework they "sometimes" leave the pipework open and this obviously fills the pipework with dust and muck even before a boiler is fitted. This would lead to a dirty system and this might explain the 2 heat exchangers going wrong, although if the things i have read about keston are to be believed then the boiler is just bad from the off. Providing plastic pipes are insulated (something i always do where possible) then they are as good if not better than copper. Just my opinion and no scientific proof to back it up Good luck

Lilly It is quite possible you have a combination of problems here. If the "o" rings have perished or failed then no it wont fix your lack of hot water, but it would stop the leak if thats where it was coming from. Ok, i had to look back to your original post to refresh my mind. Please be aware it is very difficult to dignose problems over tinternet The banging and taking off of your boiler "could" be sludge or metal particles going through the heat exchanger and partialy blocking it causing the boiler to cook and make steam pockets, hence the banging and rattling noises. A powerflush would rectify this. Your leak: if you had to repressurise after only a week then the leak should be obvious to find. One possibilty is something some people do when changing parts on a boiler ,they use the prv (pressure relief valve) to drain the boiler down enough to do repairs (this is usualy a red knob inside the boiler attatched to a 15mm copper pipe which goes outside through the wall and terminates loosely against the wall) . Often these prv do not seat themselves down properly after being opened , hence the losing of water. A test is to put a balloon over the end of the pipe outside the house which is attatched to the prv , if it fills with water then you have found your leak. Replacing the prv is the best option, messing about with it in the hope of seating it correctly is the cheap option. Now to your lack of hot water. It "could" be the domestic hot water diaphragm, these are common faults and easily fixed. If the diaphragm is split then it wont operate the micro switch to tell the boiler that you want hot water. A DHW diaphragm repair kit is approx £10 to £15 and can be sorted in a couple of hours. Its the first thing i would look at if you reported no hot water. Hope this helps and please dont hold me to anything as it is very difficult to diagnose over tinternet.

busymamae A powerflush should cost between £250 to £350 for a house that size, although having said that i live in the south west so prices may vary. Phone 2 or 3 plumbing firms or better still ask around your friends or at the local pub for recomendations. Nearly all my work comes from people talking to each other. It should take most of the day to do a house your size, 5 hours being the absolute minimum. Hope this helps

Hello everyone, my first post here. I am a qualified and registered Gas Engineer (no i do not work for BG) and i also own a Power flushing unit. I have Read this whole thread and have a few things to say: To the haters of Power flushing, please do not judge how effective this process is just by how much British Gas charge for this service. I have many many happy satisfied customers who i have done a power flush for. I charge a lot under Half the price that British Gas charge and probaly do Twice as much work and spend twice as much time. A 10 to 12 radiator house i charge between £250 and £300, this includes all chemicals and inhibitor A standard 10 to 12 radiator house will take me 7 hours from start to finish, i do it by the book and some. I believe in a fair days pay for a fair days work. If British Gas tell you that you need a power flush then please ask a couple more plumbing firms for their advise and quotes, i almost guarantee they will be at least half the price. British gas have to hike their prices up to pay the commision and show a profit. A power flush should not be used as a "this will fix all your problems" because it wont, a power flush will be needed when specific circumstances arise. This is where independant advise is vital. In answer to Lillypad2: To be honest if you are having to pressurise your system that often then where the leak is going to be blatently obvious. Even more so if it is from the boiler, that is a lot of water to be leaking somewhere. By isolating the boiler then yes it will tell you which side of the boiler the leak is coming from, he should close the heating flow and return valves under the boiler, if the pressure still drops then it is leaking from the boiler somewhere, if it stays up then you have a leak elsewhere in the pipework/radiators. If it is from the boiler then sometimes the "o" rings fail in the pipework leading to the heat exchanger, i had one like this and when i took the cover off i had 2 inches of water cover me.....that was a fun day.