Vaillant Boiler keeps turning on and off - flashing timer -> solid radiator -> flashing radiator

tencentral

I have a Vaillant EcoTech Plus 624 boiler (conventional, not combi) that keeps turning itself on and off during the night (I can hear it), and has continued today.  It cycles between:

• Flashing timer and solid radiator: 

• Just solid radiator: 
• Just flashing radiator: 
• Back to flashing timer and solid radiator

I have had a Nest thermostat for the last year and this issue has only arisen last night.  This morning I turned the Nest heat mode to Eco and the water to off (so the boiler should be off and not heating anything) - the boiler is still cycling between on and off.  Any ideas what's wrong please?  Any help would be much appreciated!

Our boiler repair company can't send somebody out for a few days due to everything that's going on, but I'd really like to know if it's worth asking somebody to come out during this lockdown.

daveyjp

Something is telling the boiler it needs to be heating, hence the radiator symbol.  The flashing timer means the boiler is cycling.  Its basically up to the temp set (66 degrees) and no further heat required.  Flashing radiator burner is operating.

It may be a Nest fault.  Are the transmitter and receiver still communicating properly?

If you need to turn the heating off press the button under the radiator symbol, the 66 degrees will come up, then press the negative button continually until the umbrella appears.  This sets the boiler to 'summer' mode and disabled the heating circuit.

tencentral

daveyjp said:

Something is telling the boiler it needs to be heating, hence the radiator symbol.  The flashing timer means the boiler is cycling.  Its basically up to the temp set (66 degrees) and no further heat required.  Flashing radiator burner is operating.

It may be a Nest fault.  Are the transmitter and receiver still communicating properly?

If you need to turn the heating off press the button under the radiator symbol, the 66 degrees will come up, then press the negative button continually until the umbrella appears.  This sets the boiler to 'summer' mode and disabled the heating circuit.

Thanks for your reply!

I think the Nest is communicating correctly - there is a green light on the heat link which I assume means it’s connected properly? 

robatwork

I have the same setup as you - same boiler and Nest. 

Bit of a long shot but your pressure is quite near the min (1 bar?). Worth topping up to the middle by opening one of the taps underneath or in the loop very near the boiler, then open another one slowly, then reverse when topped up.

southcoastrgi

 I'd be looking at the zone/mid position valve 

tencentral

southcoastrgi said:

 I'd be looking at the zone/mid position valve 

Thanks for your reply.  The engineer replaced a piece (Danfoss Randall HPA2 2 port valve actuator) - is this what you were referring to? The issue still happens with the boiler coming on when the Nest is all off (eco temp, hot water off, even restarted and reset Nest!)

tencentral

southcoastrgi said:

 I'd be looking at the zone/mid position valve 

Thanks for your reply.  Did you have this issue as well and did that resolve it?  I’m a bit worried about messing with the gas