Faulty modulation on Greenstar 18ri boiler

[Old_Badger]

Hi

I think the modulation on my Greenstar 18ri boiler is faulty.

On very cold mornings the boiler naturally reaches a higher than usual temperature during the initial warm up period. Then the boiler shuts off even when there is still demand (no fault is shown). I can make the boiler start again by turning the temperature control to maximum and then turning it back to its usual position (about 70 degrees I think).

The fault doesn't occur on warmer mornings nor later in the day when the water flowing through the boiler doesn't reach high temperatures.

The fan speed changes as the temperature goes higher, so some modulation is occurring. But maybe not enough!

I believe the modulation works by adjusting both the fan speed and the gas valve.
Does anyone know which component is most likely to be causing the fault and how could I tell?

Thanks
Mike

 

[Agile]

We don't give advice for DIY repairs on gas/combustion related matters here.

Best advice is to get a competent gas reg engineer.

Tony

 

[Old_Badger]

Okay

Are you saying that if a competent gas reg engineer agreed with me that there is something wrong with the modulation then they would be able to test my boiler and know for sure which component is faulty - the control board or the gas valve?

Mike

 

[Gas2Air]

Okay

Are you saying that if a competent gas reg engineer agreed with me that there is something wrong with the modulation then they would be able to test my boiler and know for sure which component is faulty - the control board or the gas valve?

Mike

Why would he agree with you? It needs diagnosing and then he'll give you the answer.

 

[Old_Badger]

I agree that the engineer might not agree with me, Gas2Air. But I have lived with this boiler for a long time and the symptoms tell me that a fault with the modulation is very likely. So the engineer might well agree with me.

Then we come to the real problem. Can an engineer be certain which component is causing the modulation fault?

Mike

 

[Agile]

A good engineer will be able to diagnose the fault and the cause.

That's what we do!

Tony

 

[Gas2Air]

I agree that the engineer might not agree with me, Gas2Air. But I have lived with this boiler for a long time and the symptoms tell me that a fault with the modulation is very likely. So the engineer might well agree with me.

Then we come to the real problem. Can an engineer be certain which component is causing the modulation fault?

Mike

You come across as a prat. So you go to the doctors complaining of a pain, googled it and are pretty certain what the pain is. Doc has a look and tells you it's something you didn't expect?