Boiler failing to respond to thermostat and has to be restarted

[stevered]

It has become a common occurrence that my boiler is failing to respond when the thermostat kicks in.

I hear an audible click from the heatlink when thermostat is turned up but nothing else happens.

Our heating programmer next to the water cylinder is set to continuous and all looks OK.

The only way to restore central heating is to turn the boiler off, which in turn powers off the heating programmer and pump. Turn it back on and then it fires up.

Worth noting the central heating pump is coming on when the heating is off for long periods of the time now it is cold but I believe that is just the boilers first protection kicking in as it is in the garage so will often drop below 5c.

Any ideas what could be causing this?

Here is my setup;

Vaillant EcoPlus 430
Nest e thermostat and heatlink
Honeywell ST9400A programmer
Grundfos UPS2
Honeywell V4073A1039

 

[davesparks]

Is the hot water working properly?

Does the programmer have any control of the heating? Sometimes when a nest is fitted in to an existing system you may have to leave the central heating channel of the old programmer on constantly for it to work.

 

[stevered]

Is the hot water working properly?

Does the programmer have any control of the heating? Sometimes when a nest is fitted in to an existing system you may have to leave the central heating channel of the old programmer on constantly for it to work.

Yes hot water works fine every morning.

Had nest for a couple of years now with no issue until recently and yes we always have programmer set to continuous so we can control from nest.

 

[brianmoooore]

Another boiler connected without pump over run, as in another recent thread?

 

[stevered]

Another boiler connected without pump over run, as in another recent thread?

Yes it does have pump overrun, set to 5 minutes.

 

[plugsandsparks]

Do you have a zone valve on the heating cct

 

[brianmoooore]

Are you sure that the water can circulate when the frost protection cuts in? If the pump can't move water, then it'll have a similar effect to no over run.

 

[stevered]

Do you have a zone valve on the heating cct

The only valve I know of is a Honeywell V4073A1039. Can select auto or manual.

 

[stevered]

Are you sure that the water can circulate when the frost protection cuts in? If the pump can't move water, then it'll have a similar effect to no over run.

Yes I can hear circadian and the pump comes on all the time for up to an hour when heating is off.

 

[stevered]

Yes I can hear circadian and the pump comes on all the time for up to an hour when heating is off.

*circulation

 

[brianmoooore]

Yes I can hear circadian and the pump comes on all the time for up to an hour when heating is off.

The pump may be running, but if it's pumping into a closed off pipe it will not be moving any water.
Is there a pressure sensitive bypass valve (or even a partly closed gate valve connected between flow and return before the zone valve, or is there a towel rail that heats up when the frost protection is on?

 

[plugsandsparks]

The only valve I know of is a Honeywell V4073A1039. Can select auto or manual.

Try it on manual and see if heating starts to flow

 

[davesparks]

Yes hot water works fine every morning.

Had nest for a couple of years now with no issue until recently and yes we always have programmer set to continuous so we can control from nest.

I would link out the heating channel of the programmer to see if that makes a difference, it may be that the relay in the programmer is failing and preventing the heating from coming on.

I appreciate this is a bit of a random guess approach but it will rule that possibility for minimal effort.

Do you have any means of safely testing mains voltage?

 

[davesparks]

Try it on manual and see if heating starts to flow

That won't fire the boiler though

 

[Avo Mk8]

Honeywell V4073A1039 3-port microswitch not being activated?