Faulty Honeywell V4073A 1039 Three Way Valve

[WSB]

Hi,

When I switch on my central heating the boiler does not ignite. All is fine for the hot water though.

I know these valves can stick sometimes and become faulty, especially when they get used for the first time since being off over the summer.

Been researching the subject a bit online and found out that when the central heating is switched on by the controller, it powers the motor which in turn opens the valve plus also triggers a couple of microswitches which instruct the boiler to ignite.

This makes sense but what I'm seeing confuses me. Please correct me, if what I'm saying is wrong.

With electricity switched off, I push the lever at the bottom manually, can here the motor turn, then when I let go, it springs backwards, I can hear the motor turning, presumably in the reverse direction. This sounds fair, so essentially, the valve is closed. I push the lever to turn the motor, so the valve opens. I let go of the lever and the valve closes again.

But, when I switch the power back on again (NB: THE CONTROLLER DOES NOT HAVE THE CENTRAL HEATING SWITCHED TO ON), I here the motor whirring and a couple of tiny clicks which I believe are the microswitches. At this point the boiler does not fire up.

My first thought was that the boiler wasn't firing up because the micro switch(es) to do so were faulty.

But then I go confused because I was wondering why it was opening the valve in the first place when the controller hasn't asked it to do so.

I tried out of interest to see what would happen during this state, if I set the controller to switch on heating. Nothing happened.

Any suggestions what could be going on.

Secondly, as the solution is to replace part or all of the valve head, is this model one that doesn't require draining of the water. How can I tell? Valve is in a bit of an awkward position in the airing cupboard so would rather not take the chance.

Before I start changing motor or whole head, I'd like to understand the actual problem.

Thanks in advance.

 

[ericmark]

The three port with three position valve only fires the boiler in CH mode, in DHW mode it is not energised and boiler fired direct from the tank thermostat. However you have more than one micro switch in the valve and also resistors and often a diode, so you can get some strange behaviour if those components fail.

check this

from John Ward.

 

[WSB]

The three port with three position valve only fires the boiler in CH mode, in DHW mode it is not energised and boiler fired direct from the tank thermostat. However you have more than one micro switch in the valve and also resistors and often a diode, so you can get some strange behaviour if those components fail. View attachment 171861 check this

from John Ward.

Thank you.
So you agree the behaviour I am seeing is strange?
If so, then maybe a replacement of the entire head to be sure?
Question now is whether I can do it without draining the system?

 

[stem]

With the valve at rest (power off) it sits in the hot water only position. When the heating is required, a live on the motorised valve's white wire (from the room thermostat) winds it to the first microswitch (SW1) where if the hot water is also required, it will stop. At this point the valve is in the centre position. If the hot water isn't required, it will continue on past the first microswitch (SW1) to the second microswitch (SW2) which should start the boiler. At this point the valve is at the end of its travel in the heating only position.

If you are able to do so safely, you could try disconnecting and isolating safely the white wire from the motorised valve, and see if the valve moves then when the power is restored. If it doesn't move the problem is with the external wiring, in that the white wire is being energised from somewhere when it shouldn't be.

If it does still move that indicates that there is probably a problem with the valve. Possibly failure of the first mircoswitch, which is allowing the hot water off signal on the grey wire to operate the motor when it shouldn't.

 

[WSB]

Thanks Stem,
that's a great explanation. Thanks too to ericmark too. Those videos were very helpful.
What I'm seeing today is slightly different to yesterday.
What I see now is as follows.
1: To simplify the situation I've turned the hot water on the controller to constant off which I leave off constantly throughout this description.
2: Initially, the hot water is set to constant off.
3: I disconnect all power and move the valve lever hearing the motor turn and a click for each microswitch. When released it slowly springs back and I hear the two clicks again. I believe this is all correct behaviour.
4: I reconnect the power and all the same with motor lever as described in step 3. NB yesterday at this point the valve motor was turning at this point even though controller said off (mind you, hw yesterday was on constant ON but don't believe that would have switched on the motor anyway).
5: Switched on hot water only on controller.
The valve motor turned and the grundfos pump started but boiler didn't light.
Started writing this and after some time the bloody boiler has now started. Radiators now getting warm. Typical!!!
Think I had this before but switched itself off after some time, do currently waiting to see what happens. Also need to test with hot water on constant.

Am currently hoping that this intermittent problem has gone now all loosened up.
Will update in a while.