Central Heating Problem

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funnygirl | 13:57 Wed 19th Nov 2008 | DIY
10 Answers
Our boiler keeps cutting out after 15 minutes.

We got in a mate who is a plumber (got my doubts) who says our pressure is too high which is why it keeps cutting out.

He says this will take time for the pressure to come down and then it will ok.

Has anyone heard this before??


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Is it a combi boiler?
-- answer removed --
Question Author
Yes it is a radiant!!

And the rads have been bled!
Assuming you do have a combination ("combi" ) boiler and a sealed system heating; When the water in the heating system heats up then it expands and the pressure in the system increases. If the pressure gets too high then a) the safety valve should open to vent some pressure and b) the boiler will turn off to stop heating it and stop the pressure rising.

When the system is "cold" the pressure gauge should show 1 to 1.5 bar. When "hot" it should be around 2 bar, not much more. The safety valve will probably open (and the boiler shut down) around 3 bar.

If the pressure gauge says more than 1.5 bar when cold then you need to let some water out of the system. Either via a radiator bleed valve, or via the system drain valve. If you let too much out that's OK provided you bring it back to 1-1.5 bar using the filling loop. You should bleed the air out of your radiators with the heating off (i.e. pump not running).

If there is a huge pressure rise (from below 1 bar when cold to over 3 bar when hot) then there is a fault with the system - usually the expansion vessel (which takes up the "slack" when the water expands) has failed. {Read the page below to understand about this and what you can do}.

Have a read of this - it should tell you all you need to know about sealed central heating systems (for the novice!) and faults;
No plumber of any worth is going to say "It'll come down if you leave it". That's just ridiculous.
Follow the good advice above - however if the pressure keeps rising again of its own accord, you have a serious problem with the system, maybe main pressure water is escaping into the sealed system.
If your mate does the job get some hay for his horse and a place to put his guns
Question Author
Lol @ Groupie!!

Not to worry, Mr Funny soon sent him packing.

We got a qualified man in and he is saying we need a new boiler!!!

And that is gonna cost all in around �1,800.

Thanks for all your replies and I have printed the attached doc for hubby to read!!!
Is the thrmostat working properly?
Question Author
Yes the thermo is working ok and we are still getting very hot water.
frstly, radiant bolers are realy naff and didn't sell well at all, saying that i would still get a second opinion from another qualified engineer as to whether you really need a new boiler or not as some enineers will tell you you need a new one just to make money or because its a boiler they don't understand.

the main reason for a boiler cutting out is overheating out this would happen a lot quicker than 15 mins. my money would be on the expansion vessel needing attention, are you having to top up the water in the system regularly?

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