Boiler Problem

[scoobydooby]

realised my combi boiler was dripping water earlier when I found a puddle on the floor. On investigation, I noticed the low pressure light flashing. Turned off the boiler, bled the radiators (but there was no air in them) and then raised the pressure (using the pressure thingy under the sink that the British Gas engineer showed me how to do). I switched the boiler back on but couldn't stop the light from flashing. After several minutes, the pressure started to go up - in excess of what it should have been! Have now switched the boiler off again and we've got some electric heaters to keep us warm. We have British Gas cover but I just need someone to reassure me that it's not going to explode overnight! I am a bit of a worrier.............

[Teddio]

The water leaking from your boiler is reducing the water pressure. It could be from a joint or, quite likely ,the diverter valve. The flashing light should go out if you repressurise it but will go on again later due to the water leak.
If you turn the boiler on the water pressure will rise, this is quite normal. There is a safety valve which will prevent the pressure from getting too high.

[Hymie]

You have slightly over-pressurised the central heating system. Normally a domestic boiler will operate at 2 Bar. The boiler will be fitted with a pressure relief value which will operate & relive the pressure should it exceed a set level (normally around 3 Bar). So the boiler will not explode, even if you were able to operate it.

From what you say, it sounds like your heat exchanger (in the combi-boiler) is leaking (in the central heating section). Bear in mind that the boiler is likely to leak more, until the pressure has dropped significantly.

Now the bad news � a heat exchanger can cost over �300 and that does not include fitting. You could be looking at a repair costing over �500. If you have British Gas cover and it covers this repair, you can consider it repair insurance well worth having in this instance.
Normally such insurance repair policies do not cover parts that can break.

[scoobydooby]

Thanks all. I'm hoping my insurance covers it........I pay top whack and have it serviced every year, so here's hoping! The only reason I increased the pressure was to satisfy myself that I wasn't calling an engineer out for something that was my fault (I have been told to check the pressure and adjust if necessary, and thought maybe I hadn't done enough).......these insurances don't cover us for ignorance......and after all, I don't pretend to know anything about plumbing or electrics.......that's for the professionals.

[gucciman]

i'm not quite sure how someone can diagnose the leak is coming from the heat exchanger without visually examining it, it could be the heat exchanger but the leak could be coming from any number of different places/joints, the majority of leaks we see are not from the heat exchanger.
the majority of combis are pressurised to 1.0 bar when the boiler is not running (vaillants are 1.2 bar) when you operate the boiler the pressure will immediately rise to 1.5 bar due to the pump pressure, upon heating the pressure may rise to 2.0 bar, this is normal, if the pressure creeps up to over 3.0 bar then as already said the pressure relief valve will open up and dump the water out of the boiler, the boiler will probably then go to lock-out and need re-filling and re-setting.
you said that it took several minutes for your pressure to start rising. this has already said could be because you have not closed off the filling loop properly or it could even be a faulty filling loop and it wont close off properly (with the exception of vaillants most taps on boilers seem to be designed to never be used, use them and they leak) quick way to check that the filling loop is closed off is to unscrew it and see if its dripping still.
the main reason we see for the pressure creeping up is the expansion vessel which needs repressurising, a job for an engineer.
its very doubtful as british gas would have spotted it but we do come across a lot of boilers where the installers have not bothered to connect the pressure relief pipework to the valve (the pressure relief valve is meant to dump the water safely outdoors by running a pipe thru the wall) so if the pressure does rise over 3.0 bar and the prv opens up it dumps water all over the floor.

[gucciman]

its also worth mentioning that if the prv does open up they are a ****** for not closing again due to sludge/debris in the system getting stuck in the valve seating, your left with a drip then, you can check for this by tying a clear plastic bag over the end of the pressure relief pipework and seeing if it catches any water.
the boiler wont explode as they contain many safety features to prevent this. depending on how quickly your boiler is losing water it should still be safe to use i.e. if your only having to top it up every couple of days, if the waters ******* out as soon as you fill it then switch it off and get british gas out.
oh and if you do fill your boiler up and accidentally fill it too much then just open one of the bleed vents on a radiator and catch the water in a saucepan until the pressures dropped back down.