Nest - Central Heating Problem

[Rich2020]

I have a Nest gen 3 Gas C/H system in a standard size semi. Up until a couple of days ago, the hot water and central heating worked fine. The schedule and app on phone triggered as should. Nothing has changed in the house whatsoever. The thermostat and the Heat-Link(receiver) are paired so I happy with that.

As of now, the hot water works but not the central heating. If I set the temp on the thermostat up beyond current temperature then the pump kicks in and the Thermostart turns Orange and the display shows 'heating' but the Boiler doesn't fire up. However if I press the button on the Heat-Link(receiver) this sucessfully turns on the hot water and heating and so I get both heating and hot water but not if I scheduled the heating or turn up the thermostat.

Nest Customer Care point me to the valve being the possible issue but the Honeywell V4043H valve is a 2 way port Auto/Max Open which is for the hot water only. I am certain this is not a mechanical issue of a kind but must admit I am somewhat unclear.

Any ideas or what I should be looking for would be welcomed if you would please?

 

[justbigboned]

Not a plumber or heating engineer but I do have a Nest and have fixed a few issues with my system over the past few years.

What type of heating system do you have?

It does sound like a zone valve. My system is S plan so I have two zone values, one for heating and one for hot water. My central heating 2 port valve died and caused the exact symptoms you are describing.

 

[muggles]

I agree with Nest tech support. Sounds like a faulty zone valve

 

[Deleted member 267285]

If you have one only for hot water, you’ll probably have one for heating, so you could try to locate that and go from there.

 

[Rich2020]

thanks JustbigBoned & muggles, will check valve. Just the one vale Chris_W.

 

[ianmcd]

Find your wiring center and have a look in there, if you have two grey wires joined together and 2 orange wires joined together then you do indeed have two zone valves, it would be unusual to have only one but have seen it, you say the zone valve is on the HW , if you only had one zone valve then everytime the HW was on the CH would also come on so if it worked OK before then you definately have 2 zone valves

 

[ericmark]

My plumber was talking about if really needed zone valves on CH, I did fit them, but he is correct when he says the TRV is a zone valve, so theory zone valve and TRV is doubling up and not required.

Except some way the heat link or boiler needs to know if the zone valves are open or closed, and there are no micro switches on the TRV's.

So with Hive, EvoHome, Wiser, or Tado the plumber had a good point, but Nest does not have any link to TRV heads as far as I am aware?

I would guess Nest is opening a zone valve, and the zone valve micro switch is failing to start the boiler, but Nest may not connect to a TRV but it is rather versatile in other ways, including opentherm, so without knowing how wired hard to be sure what has happened.

 

[Rich2020]

@ianmcd @Guys Apologies.... The Valve controls both hot water and central heating sitting on a T marked A, B and A+B in middle. When the schedule for the hot water triggers the system fires up the boiler, I turn the thermostat for the heating and the rads warm up. However the valve tick tocks like a clock. This is the only way in which the heating to the rads works as without the hot water being turned on, then the central heating won't work. Sorry

 

[ianmcd]

@ianmcd @Guys Apologies.... The Valve controls both hot water and central heating sitting on a T marked A, B and A+B in middle. When the schedule for the hot water triggers the system fires up the boiler, I turn the thermostat for the heating and the rads warm up. However the valve tick tocks like a clock. This is the only way in which the heating to the rads works as without the hot water being turned on, then the central heating won't work. Sorry

No worries lad we are getting there, what you have is called a Y plan system, normaly when the valve ticks it means that the HW off has a fault, so you have one 3 port valve , are you sure that absolutely nothing has been changed ? I get a feeling that something has, with the system you have , you need a HW off connection,is there a connection on your nest that has a wire in terminal 4 of your nest

 

[ianmcd]

nest wiring

 

[Rich2020]

the ticking only occurs if hot water and heating engage. if just hot water then no ticking. not touched the system so nothing has changed, nor the wiring. always been okay until last few days. motor within honeywell v4073a maybe issue? not engaging cog within and so turning valve? (just guessing)

 

[ericmark]

I have had it in the past where if you move the bleed leaver on the motorised valve and latch it open it will work, it is not a fix as every time it asked for DHW the CH comes on, but it will likely keep things running until after lock down when you can get the head changed.

 

[Rich2020]

@ericmark I tried this as you said but not effective as lever reverts to auto position and unable to fix lever into place as definitely doesn't lodged under ratchet.

 

[ericmark]

The one I used looked like this

and you could lift leaver and hold up once at end of travel and it would latch in open position, sorry if that does not work with yours.

 

[ianmcd]

the ticking only occurs if hot water and heating engage. if just hot water then no ticking. not touched the system so nothing has changed, nor the wiring. always been okay until last few days. motor within honeywell v4073a maybe issue? not engaging cog within and so turning valve? (just guessing)

No you have a HW off signal fault somewhere, that is why it is clicking