Boiler stops when on HW only

[WoodleySaint]

Hi,

I have a problem with our gravity fed Potterton Profile 80e boiler whereby if the controller/timer is set to Hot Water the boiler will fire up and run for a 3 minutes and then cuts out and wont fire again. If the controller is then set to Central Heating it will run perfectly well, never cuts out.

Any ideas on what is happening?

Thanks for any advice

 

[Agile]

How long are you waiting for it to come on again?

It can easily be 10-15 min.

Your pipes are probably rather sludged up and reducing the gravity flow!

Tony

 

[WoodleySaint]

It fires up again after 30 minutes. I think the flow is OK as the radiator, which is fed off the HW flow, heats up.

The whole system was drained down last summer as a radiator was moved so I would hope it's not gunged up already!

 

[James1991]

Check the ball valve on the F&E tank hasn't stuck.

If the tanks full of water then it could be the cold feed is blocked where it connects in to the pipe work.

Go to the highest radiator and open the bleed valve. If nothing comes out then it could be either.

Some old gravity systems were fitted with mechanical pipe thermostats on the return pipe. If it's got one, it could be stuck.

 

[WoodleySaint]

Over the weekend I drained the system down and refilled. The water which came out was clear and it refilled without issue. (Had to bleed a couple of rads but that is normal.)

There isn't any thermostat on the return pipe and the one on the flow side, which is within the boiler cabinet, was replaced last year.

Any other suggestions folks?

 

[jeff the gasman]

Check the ball valve on the F&E tank hasn't stuck.

If the tanks full of water then it could be the cold feed is blocked where it connects in to the pipe work.

Go to the highest radiator and open the bleed valve. If nothing comes out then it could be either.

Some old gravity systems were fitted with mechanical pipe thermostats on the return pipe. If it's got one, it could be stuck.

+1 and cold be blockage in primaries. Sludge etc.

 

[jeff the gasman]

Sorry I didn't read the thread completely.
It sounds like an airlock in the primaries. Letting the boiler boil for a couple of seconds should cure it.

 

[WoodleySaint]

Sorry I didn't read the thread completely.
It sounds like an airlock in the primaries. Letting the boiler boil for a couple of seconds should cure it.

Excuse my ignorance, how do I make it boil for a couple of seconds?