Boiler failing to respond to thermostat and has to be restarted

[stevered89]

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

 

[Jajodu]

What does the boiler display show when it happens? Press the i button to see the boiler state.

 

[stevered89]

What does the boiler display show when it happens? Press the i button to see the boiler state.

No fault codes seen on the boiler or errors on any other component. The only thing I noticed in the diagnostics menu is that heating mode status = blocked when it doesn't turn on, then I restart and it changes to released when it starts firing. However I looked this up and all that means is released = thermostat calling for heat, blocked = thermostat not calling for heat

 

[CBW]

Sounds more likely to be the 3 port valve than the boiler. Probably not making the microswitch inside.

 

[stevered89]

Sounds more likely to be the 3 port valve than the boiler. Probably not making the microswitch inside.

I guess that would also explain why the pump is coming on randomly throughout the day sometimes for an hour at a time?

 

[stem]

As well as the frost protection, you say you have a hot water cylinder, so, if the HW is set 'on' at the programmer, the 'random operation' of the boiler / pump could be that.

A fairly simple test is when the fault occurs and the heating isn't running when it should be, is with the hot water on too, to turn up the hot water cylinder thermostat to max so that it clicks on and the boiler and pump start up. If the radiators also start to warm up then, the microswitch inside the motorised valve is the culprit. If they don't warm up, it's something else.

 

[stevered89]

As well as the frost protection, you say you have a hot water cylinder, so, if the HW is set 'on' at the programmer, the 'random operation' of the boiler / pump could be that.

A fairly simple test is when the fault occurs and the heating isn't running when it should be, is to turn up the hot water cylinder thermostat to max so that it clicks on and the boiler and pump start up. If the radiators also start to warm up then, the microswitch inside the motorised valve is the culprit. If they don't warm up, it's something else.

Hot water is set to auto and comes on between 0700-0730.

Good idea with that test though, will set hot water to continuous next time it happens and see if heating kicks in.

 

[Jajodu]

If the display shows s30 when it should be heating then it's your external controls at fault.

 

[stevered89]

If the display shows s30 when it should be heating then it's your external controls at fault.

No it does not show any codes

 

[stem]

Will set hot water to continuous next time it happens and see if heating kicks in.

Just setting the hw to continuous is not what I suggested and probably wouldn't work. Read my post again more carefully.

 

[Jajodu]

No it does not show any codes

Did you press the i button?

 

[stevered89]

Did you press the i button?

I've been through every menu and setting including installer level.

 

[Jajodu]

That's not what I meant. When you're expecting the boiler to fire up and you press the i button, what does the display show?

 

[stevered89]

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?