Overheating Worcester combi

[jabberwok]

boiler: Worcester 240 combi RSF (about 2/3 years old)

All of a sudden our boiler wouldn't fire up for either the heating or hot water. It made the noises indicating that it may light any minute, but the pilot light just never sparked. After a little reading I discovered that it may have automatically switched itself off due to overheating, so I pressed the reset switch and hey-presto it fired up ok. However, after a few minutes it switched itself off again and the reset switch popped out.

I've tried turning the thermostat right down to minimum, but both the hot water and radiators get very very hot. A very tiny amount of water is also dripping from the bottom of the boiler. The boiler also sometimes made a screeching noise (i guess the pump?) - could this have contributed to it's failure?

The pressure on the gauge is just over 1 bar.

Can anyone suggest possible causes/solutions (if there are any!)?

thanks very much

 

[ChrisR]

Is the boiler on even with the CH wall thermostat turned down and no tap open, while it's doing this?

 

[jabberwok]

hi ChrisR - Yes the boiler remains on, but i don't have a wall thermostat - only the temperate control dial on the boiler itself.

What I've done is turn the central heating to the 'on' position, turned the hot water to 'off' and turned the temperature control right down to 'minimum'. After leaving it like that for a few minutes the radiators still getting incredibly hot and the boiler just shuts itself off (the reset switches pops back up).

Could it be a sludge/air blockage problem? would bleeding the entire system help in any way? When we first moved into the house there was a slow leak, so for a while we kept refilling the system every 2 weeks or so.

 

[ChrisR]

Diverter valve is possibly stuck in the hot-water-providing position. So the boiler thinks it's providing HW but it actually heats the rads. Boiler looks at the HW temp sensor which doesn't get hot because the water's not going that way, so it gets hotter, & hotter....

It would depend on the boiler's wiring, but the boiler may heat the rads if you turn the CH off, as well.

SOmetimes the stuck valve will come free if you turn the hot tap on & off several times. Turn the CH off & try it.

 

[jabberwok]

Tried as you suggested, turned the hot water on/off about 5 times (do i have to let it fire up fully before turning off each time?), then turned the tap off and turned the heating on (still with temperature control dial at 'min'). However, the radiators still burn up. The hot water also seems to be a lot hotter than I ever remember it being.

Is there any way to budge the diverter valve manually (bearing in mind that I'm an uber-amatuer )?

 

[jabberwok]

Ok Chris, I'm pleased to say that the boilers now working! I think the tap cycling you suggested did after all do the trick, so thanks very much indeed - you've saved us from having a cold, cold xmas!