New pump but boiler stops firing before room temperature is reached.

[Agile]

The boiler should be heating the flow up to what it is set at and so up to 80 C.

Under the pump pressure the boiler should create a flow through the rads and the heat loss from rads should result in a return temperature of about 70 C.

All temps approximate.

Why don't you call an engineer.

Tony

 

[SJRSJR]

Thanks, am trying to understand and eliminate the more straightforward causes for myself. If the flow was say, 80C, but the return differential greater than 20C, would that suggest a problem with the balancing? And would the boiler cut out because its thermostat has failed and it thinks it's hit its temperature when it hasn't?

By the way, I'm not getting any error message on the diagnostics (Halstead Finest Platinum)

 

[Agile]

The boiler tries to provide the set flow temperature. You seem to be confusing the room stat with the boiler flow stat.

Once reached it reduces the power input.

If the minimum power input is still too much the boiler turns off and stays off until after the anti cycling delay has ended.

 

[SJRSJR]

I was referring to a possible problem with the boiler stat, the room stat appears to work at the lower end, just not at the top temperature. In lay person's terms how do you manage the minimum power input being too much? Thanks.

 

[steve32]

I would be looking for a blockage most likely heat exchanger

 

[Agile]

If the system does not absorb the boiler minimum heat output then it has to go into on/off modulation.

It then stays off until the flow temperature has reduced below the set value and the anti cycle delay has expired!

Tony

 

[Jajodu]

Hi. After the combi boiler pump failed I was feeling pleased with myself for flushing the CH system and changing the pump head (Grundfos UPS2 15 60). I would have liked to have changed the whole pump because the pipe was a bit cruddy but access to the nuts was difficult. Overall though the drained water was very clear so I didn't bother with any cleaning fluid, just inhibitor.

It was a relief to have the heating on and get hot water again. However even with the room thermostat set to 30 the boiler switches itself off well before then (I can hear the thermostat dial 'clicking' at 20). It fires up again after a while but only for a few minutes before switching off. It's maintaining warm but not hot radiators. All have been bled and TRV valves are fully open. The radiator and hot water dials on the boiler are on max. I don't have a thermometer but the flow and return pipes are similarly warm to touch. The hot water is working okay. Does the pump drive HW and CH or just CH?

Before changing the pump I hadn't noticed a firing up problem but I knew the radiators weren't getting hot and assumed it was all pump related.

The boiler is a Halstead Finest Platinum (12 years old). I know it will need changing soon but I'm trying to eke it out through the summer. Any thoughts on the likely cause and what I can do to resolve it? Thanks.

Just to be certain, is it the room stat you hear clicking off at 20 deg when you've set it to 30 deg?
If so it looks like a very faulty stat.