Boiler wont stay running

[oilman]

I have a Glow Worm Ultimate 50BF Boiler, its about 15 years old but normaly works fine.Recently after being on for a few hours it shuts off & eventhough the room stat & boiler stat are calling for heat it wont fire up.The motorised valves are working ok when I alter the thermostats.The boiler stat has always been set to full.The system has a 3 speed pump that has always been set to speed 1.When this problem occurs the boiler will fire up and run normally if I set the pump to speed 2 or 3.Could this be a pump fault or possibly a boiler stat problem.Any advice would be gratefully received.

Thanks

 

[Apache]

Any advice would be gratefully received.Thanks

A duvet, bottle of wine, make your own heat?

:worship

Sorry, can't help, but welcome

 

[Sidewinder]

Is this a "combi" if so check the pressure?

Can't think right now what the boiler is & have to dash.

---------- AUTO MERGE Post added at 16:55 ---------- Previous post was at 16:55 ----------

BTW, Welcome!

 

[sellers]

For things like internals its best ringing up tech dept. They can run through with you a diagnosis checking voltages on certain terminals and resistances across sensors. Sounds to me like a fault with the pump if its fine on the other 2 speeds but best to ring up.

 

[oilman]

Thanks Sidewinder,no its not a combi is a good old fashioned thing with a pilot light

 

[NozSpark]

Sounds like a boiler fault to me...

IIRC British Gas used to do a one off repair for

 

[wozz]

Sounds like a boiler fault to me...IIRC British Gas used to do a one off repair for

 

[sparkytim]

Have you checked the water level in the system?.

Have found if water level dropped by slow leak and ball valve on top up tank stuck then system not refilled and cuts out on Boiler stat due to over heating.

Take a look in your loft and see if Top up tank is empty (Smaller tank of two)

 

[PC Electrics]

Most modern boilers require the pump to be on full speed. Yours, being a cast iron heat exchanger won't be so critical, but my best guess is that the water flow on speed 1 is not sufficient to remove the generated heat and the boiler is cutting out because it is getting too hot (especially now it's working harder in the cold) - use 2 or 3.

 

[oilman]

I think that as the system has worked fine since I speeded up the pump that this is the case and would also be the reason why the problem only starts after the system has been on for some hours,I just wonder why it hasnt done this before as it has run on speed 1 for a good few years.

Thanks for the advise.

 

[kme]

Agree with PC - pump speed should reflect the type of heat being provided - i.e.

If you have coal CH, the pump should be on slow speed, because its a constant heat. With gas, you have instant heat (and pretty much instant cold), so the pump needs a faster speed to move the heater water to the rads before it cools too much. Pump on high speed should be fine (its also possible that the pump has sludged up a little, and the slow speed has got a little slower than it used to be; resulting in the boiler internal thermostat shutting heat down, because the heat builds up in the boiler......

 

[septiclecky]

I think that as the system has worked fine since I speeded up the pump that this is the case and would also be the reason why the problem only starts after the system has been on for some hours,I just wonder why it hasnt done this before as it has run on speed 1 for a good few years.Thanks for the advise.

May be sludge in the system that has built up over the years is causing the problem as restricting flow of water through the system sounds like it the system needs flushing out

 

[PC Electrics]

I think that as the system has worked fine since I speeded up the pump that this is the case and would also be the reason why the problem only starts after the system has been on for some hours,I just wonder why it hasnt done this before as it has run on speed 1 for a good few years.Thanks for the advise.

Almost certainly silt / corrosion / debris settled in the bottom of the heat exchanger - this slows the heat transfer. A power flush would sort this and extend the life of the system considerably.

(although it is arguably better to put the power flush money towards a new more efficient boiler, that way you'll save the money back in saved gas)

---------- AUTO MERGE Post added at 07:52 ---------- Previous post was at 07:50 ----------

In fact having the pump on slow speed promotes the settling of debris in the exchanger more so than a higher speed

You could try a manual flush yourself - materials are cheap but it's a lot of effort.