Combi boiler not maintaining water pressure

Hi there, I could do with some friendly advice please. I have a Chaffoteaux & Maury Britony Combi 80 (or possibly 100) and have had snags with the hot water ever since I took the rad off the wall in my bedroom in order to paint behind it. Followed careful instructions and got the rad off no problem. Unfortunately, I hadn't quite turned off the control valve all the way and I experienced some leakage around the open pipe end which seemed to get worse whenever I ran any hot water (which was taking incresingly longer to warm up). As a precaution, I turned off the hot water and have not run any since and that seemed to solve the leaking issue. Once I'd finally noticed that the control valve was not off all the way (how blonde!), I closed it fully and tightened the compression joint underneath to make doubly sure. I then noticed that the pressure gauge on the boiler was at 0 bar and so I opened the filling loop valve to top it up, like I'd been shown before I moved in. The pressure went straight up to almost over 3 bar and when I close the filling loop again, it went almost straight back to 0. I opened the filling loop once more to try again and looked out my bathroom window at the same time to see water gushing out of the overflow pipe and down my outside wall. Have I managed to somehow fook my hot water/boiler/whatever by taking the rad off the wall and not doing something else as well to prevent this happening?! Any help would be greatly appreciated.

The problem is that your pressure relief valve is open. If you're losing water that fast it sounds like it's fully open. Did anyone tell you to open this as a method of draining the system before removing the rad? if so this was bad advice.

You can always try closing it but it's likely that it won't reseat itself properly and will need replacing.

ArtfulBodger said:

The problem is that your pressure relief valve is open. If you're losing water that fast it sounds like it's fully open. Did anyone tell you to open this as a method of draining the system before removing the rad? if so this was bad advice...................

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As I understand it, opening the PRV to ensure it isn't stuck is part of the BSS7074 part 1 service checks on sealed heating systems. I always check the safety valve operation, otherwise how do I know it isn't stuck?

Checking the operation of the PRV and using it to drain the boiler are somewhat different.

I didn't touch anything on the boiler before I removed the rad but I think I can locate the prv from the diagram in the manual so I shall check it to see if for some reason it is open. I'm wondering if I bit off more than I can chew cos I just followed the instructions in my humble DIY manual and I've no idea if by opening the filling loop too quickly perhaps I might have damaged the prv! I will also phone the guy I bought my house from and see if he can tell me when the boiler was last serviced.
Thank you very much for the advice, I shall have a look and see what I can do.

don't start taking the boiler apart to find the prv - that would be unneccessary and dangerous. identify the pipes coming in/out of the boiler. one of them is an outlet from the prv. it probably runs to a drain gulley outside.

put a container underneath it and then refill the system. if your container has water in, then it's stuck open.

PRV is a job for a corgi bloke, they're important safety devices, so if you suspect it, call a gas man (or woman)

On looking in the manual, the prv is among all the pipes at the bottom of the boiler and so I would not have to take it apart at all - besides, I know where my limits are and I have no intention of trying to get into the boiler when I've no idea what I'm doing! I think I'll be having a good flick through my yellow pages tonight - thanks for the advice, I've really appreciated it!