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

 

[oz-plumber]

Are there battery's in the thermostats that need replacing?

 

[stevered]

Are there battery's in the thermostats that need replacing?

No, nest e is mains powered and heatlink has brand new batteries. No errors on any component.

 

[oz-plumber]

Next thing: I hope your confident with a multimeter or voltage tester.

It could be the boiler PCB, but I wouldn't replace it without testing everything first with a multimeter

 

[stevered]

Next thing: I hope your confident with a multimeter or voltage tester.

It could be the boiler PCB, but I wouldn't replace it without testing everything first with a multimeter

Yes I have read it could be that. Makes sense that it only responds after boiler restart. Could that be causing the pump to run for long periods when the heating is off as well as I think frost protection shouldnt activate the pump it should just circulate 10c water around the boiler when the boiler temp falls below 5c? Anything else it could be as I will probably get a gas engineer in?

 

[Basher]

The Honeywell valve listed is a 3 port.
So is this a Y plan system?
If so, might the problem be the microswitch in the 3 port valve head not being activated to power the boiler, because the mechanism is stiff or worn or the motor is weak?
The motorised head is replaceable if the valve part is operating freely.

 

[stevered]

Honeywell V4073A1039 3-port microswitch not being activated?

OK so I looked at the microswitch last night and realised it was set into the middle position.

Have changed to be locked in to auto and heating came on first time last night without restarting the boiler.

However in the early hours of the morning from 0500 onwards and throughout the day the pump is still operating without heating or hot water being on.

The pump just came on now and checked the boiler and it wasn't firing up or anything and the boiler temp was 13c so frost protection wouldn't have kicked in.

Just need to stop the pump randomly coming on now so maybe I do need a new microfilter?