Boiler firing, but not when it should

[JohnMo]

I had a similar problem on a gas boiler.  My buffer was set for 40 deg, but the boiler which was set at 45 deg and would never fire up, until the temp dropped in buffer to quite a bit below 40. 

 

What was happening, the boiler pump would start, and the boiler was not seeing a big enough difference between the return flow and the boiler temperature set point, to allow the logic to give a firing permissive.

 

Once I had increased the firing temperature, it work fine.  So as said you will need to find the sweet spot by increasing the boiler set point 

[vala]

@Temp @JohnMo

thanks for that explanation.

I think it's now solved but maybe smaller jets still needed, if there's a need to charge the buffer to 70°.

I turned up the boiler stat to max (77°) and the buffer wouldn't get up to 70°, would get to 68-69°. Yet there was still 240v from the relay to the boiler. Thinking the controller still deemed it to be 'on' as it hadn't reached the satisfied temp on the controller.

Reduced the off temp of the buffer to 65°, and relay to the boiler is now 0v. Think this is right now as the boiler stat was limiting the buffer max temp to be around 68-69°.

And it is allowing temp to drop in the buffer. I left the house and flow was showing 69°, return 43° on the buffer. And the flow needs to see 40° before the boiler should fire again and charge the buffer.

I shall see how it is tomorrow when I get to the house.

[JohnMo]

Great

[Temp]

1 hour ago, vala said:

think it's now solved but maybe smaller jets still needed, if there's a need to charge the buffer to 70°.

 

I wouldn't rush to fit smaller jets. That was last resort for us before fitting a bigger thermal store or smaller boiler.  Try turning up the boiler stat and possibly experiment with the pump speed first.

 

 

[vala]

@Temp

No won't be rushing. Just keeping it as an option should the need arise.

We've still got the downstairs UFH to go in at some point in the next couple of years so that may help in getting rid of the heat produced.

Tbh at present I'll probably just leave the buffer set to turn off at 65°. We'll just monitor it to confirm all is working as it should.