Boiler not always starting

Hi,

I have a Woodpecker 25 biomass boiler, but I don't think the fact it is biomass that is the issue. When running, the boiler is great.

My problem is that when my water tank is cold, and the tank thermostat is calling for heat the boiler won't always attempt to start. It fires OK when the boiler is >5 oC colder than it's set temperature (80 oC), but if the tank has had a lot of heat drawn off, and the boiler is still up to temp, it stays off.

It wasn't a problem until a few weeks ago, when it was timed to come on just in the evening. But found we were running out of hot water and needed it on in the mornings too.

So now it fires up in the morning @ 07:00 stays running, or modulating till 10:00 - All good as the boiler is in the garage and cools below set point overnight, BUT, in the afternoon @ 16:00 it is sometimes still warm enough at the boiler so wont try to start even though the tank is cool enough. To get around it when I get home from work, I just switch it off and on again, this sequence starts the pump at the back of the boiler which draws off enough hot water enough to kick it into life.

My question is, should the tank stat be starting the boiler under these conditions, or, as I think would make sense, start the pump at the back of the boiler, which would itself then pull the boiler on?

I hope this is all clear and not too long, Thanks in advance Mike.

Tank stat should be set at 60-65 degrees.

Thanks for replying. Tank stat is actually set to 75 degrees.

That shouldn't make any difference though - should it?

The temp actually falls to ~40 ish degrees and still won't pull boiler on as boiler is still warm.

Is there a pump over run on the boiler?

This would dissapate the heat from the boiler after it had finished firing and so ensure it would fire on the next demand.

Ted

kittedup said:

Is there a pump over run on the boiler?

This would dissapate the heat from the boiler after it had finished firing and so ensure it would fire on the next demand.

Ted

Click to expand...

Good point, I don't think there is, but that should cure the problem.

I'll check, Cheers.

I can confirm the boiler doesn't have a pump overrun facility.

I'll get in touch with my friendly sparky (not the one who fitted it) and see if he can re-wire the tank stat or something.

Cheers again, light @ end of tunnel

It is possible to wire up a pump over run.

But I suggest you ask the makers for advice as too much cooling of the boiler can cause condensation and corrosion.

When the demand for heat ceases how long does it take for heat generation to cease? Is the pump stopped immediately the demand is ceased?

Tony

When the heat demand is reached, the boiler goes through an "extinguish" phase and it all shuts down, waiting to be called.

After the suggestion on here about pump overrun, I googled and found this thread http://community.screwfix.com/threads/pump-overrun-wiring.86665/ # 20 is the relevant one. Have spoken to sparky over the phone and he said it sounds like it should work.