Y Plan, no heating

[Brian Johnson]

Hi Folks,

Sorry if this is a regular topic ...

Y Plan with Honeywell V4073A valve and Towerchron QE2 programmer 03.04.00.0005.1

Hot water fine but no heating. When turning on heating, valve moves and light on pump glows for a second or two and then goes off. The white wire to the valve is powered (heating on). Replaced the valve with brand new item, no difference. Noticed though that the grey wire is live (Hot water off) whether the hot water is off or not. Both the cylinder stat and room stat seem to be OK.

Currently turning both hot water and heating on at the same time and getting both hot water and heating (guess that's the mid position setting) ... soon as I switch the programmer to 'just' heating, nothing at all. After not solving the problem with the new valve, don't really want to now fork out for a new programmer but wondering what else it could be ...

Thanks for any ideas, checks and so on and best regards

Brian

 

[stem]

You seem to have a fair working knowledge of the valve and you have checked the first things I would have advised. The Hot water 'off' grey wire is energised from both the programmer and also the cylinder thermostat (when up to temperature) so it can still be live when hot water is still set 'on' at the programmer.

In 'hot water only' and the mid 'hot water and heating' position, the boiler is energised via the hot water cylinder thermostat. When only central heating is required the valve winds fully across and a microswitch energises the orange wire leaving the motorised valve. This orange wire is what is responsible for running the boiler and pump when only the heating is required.

The orange wire should connect to the boilers switched live supply. Which will be linked to the hot water cylinder thermostats 'call for heat' terminal also.

The orange wire is in turn fed from the white wire which you say is live, if so, and if the valve is winding across to the heating only position, I would be checking the connections between the orange wire and the boiler.

 

[Brian Johnson]

Thanks stem, great explanation and I'll check that out on Wednesday (my daughter's house). Do you think I can rule out a programmer fault?

 

[stem]

Yes, I think so. The programmer supplies a switched live to the room thermostat, and the room thermostat in turn passes it on to the motorised valve's white wire to move the valve from the rest position (which is hot water only) to one of the heating positions. If the white wire is getting a live and moving the valve, then that is coming from the programmer via the room thermostat.

As I understand from your description, the valve is positioning itself as it should, but that the boiler / pump come on in 'hot water only' and 'heating and hot water' positions, but not in 'heating only'

 

[stem]

When you said replaced the valve, did you replace the whole thing, or just the head? If just the head, it may be that the mechanical part is preventing the valve completing its full travel and energising the orange wire. To test this if you can remove the valve head and try the heating only with the head off. Does the boiler and pump operate now? If you have changed the whole valve you can ignore this suggestion.

When turning on heating, valve moves and light on pump glows for a second or two and then goes off.

This is a bit of an odd symptom. Normally the motorised valve's microswitch works on a 'snap' principle, operated by a spring, which usually means it either operates properly or it doesn't operate at all, but nor partially in the way that you describe, which is why I'm thinking more towards the wiring between the valve and the boiler. Depending on your boiler, the pump may be controlled by the boiler, but if yours is, and there is a fault with that part of the circuit, the same thing would happen when it was heating just the hot water.

 

[Brian Johnson]

First of all just changed the powerhead. No joy so then changed the whole thing. The boiler is an ancient back boiler ... not a Baxi, might be Glow Worm. Chances that we have two poor valves seems unlikely (?) so I'm going to check out the Orange and chase that through the wiring ... using the V4073A wiring diagram ... though have to say that the wiring isn't great, several boxes with individual block connectors inside - even used a sleeved earth to carry live!

 

[stem]

The boiler is an ancient back boiler

Then the pump and the boiler will both be powered directly from the orange wire.

Chances that we have two poor valves seems unlikely (?)

Indeed, especially as it is an unusual fault. The chances of it occurring with two valves is pretty slim.

so I'm going to check out the Orange and chase that through the wiring ... using the V4073A wiring diagram ... though have to say that the wiring isn't great, several boxes with individual block connectors inside - even used a sleeved earth to carry live!

Seems like a good place to start. If that doesn't yield any joy, then a check of the white wire again just to make sure that it provides a continual, stable supply when the heating is calling for heat would be next.

 

[Brian Johnson]

Hi stem,

Sorry it's taken so long to get back to you. I think I now have the problem understood. I think I have proven the problem to a faulty programmer. To get the heating to work (on CH only) needs both the white and the grey wires (on the V4073A 3 port valve) to be energized ... it's power on the the grey that drives the valve from mid position to fully open to operate the microswitch to power the orange wire to power the pump and boiler ...? With the HW off, power is delivered to the grey wire from the programmer ... and there's no power on the grey ...

... so I removed the programmer and with HW off, applied power directly to both the white and grey wires and hey presto, the heating fires up. The info was all there, I just hadn't put it all together. Looking for another QE2 Programmer on Ebay ...

Best regards and full marks to stem for setting me off in the right direction!

Brian

 

[stem]

To get the heating to work (on CH only) needs both the white and the grey wires (on the V4073A 3 port valve) to be energized ... it's power on the the grey that drives the valve from mid position to fully open to operate the microswitch to power the orange wire to power the pump and boiler ...? With the HW off, power is delivered to the grey wire from the programmer

That is all correct.

... and there's no power on the grey ...so I removed the programmer and with HW off, applied power directly to both the white and grey wires and hey presto, the heating fires up.

Then it sounds like you have found the problem. Well done! It certainly helps when you are able to understand how it works. IMHO the three port valve is a pretty clever piece of engineering. It can take a bit of getting your head around, but I would take my hat off if I had one, to whoever came up with the design in the first place.

 

[flameport]

Looking for another QE2 Programmer on Ebay ...

Why? - it's a current model and can be purchased new from many suppliers.

 

[Brian Johnson]

I'm not buying second hand. A new unit, on EBay is £37.50 (free delivery)... Amazon £10 more .. other suppliers similar to or more expensive and not clear if there are delivery costs. It's my daughter's house - they understand the unit so think it makes sense to get another ...

 

[stem]

Having just re-read your original post, something still doesn't quite sound right. When you were describing the original problem of "no heating" You said:

The white wire to the valve is powered

and..

The grey wire is live (Hot water off)

As you have determined, this is as it should be in order for the 'heating only' condition, and why I thought the programmer was unlikely to be faulty, as both signals were present, but you said that the heating wasn't operating in this condition......

...and of course, it is the same as:

applied power directly to both the white and grey wires and hey presto, the heating fires up.

and the heating operates.