Need some diagnostic assistance.

[BigJohnD]

Hot water is not circulating through the radiators.

Hot tap water is fine, pump works and the boiler works fine.
I've over-ridden the clock, i.e. CH is on constantly.
I've set the thermostat to 25° with the ambient temperature around 15°, and it indicates "On".

The motorised valve (a standard V4073a) does not seem to work.
If I push the lever to open the flow to the central heating, the pump does not start, nor does the boiler fire up.
However, if the pump is running to heat the hot water, leaving the valve jammed open allows water to flow through the radiators.
When the water in the cylinder reaches the required temp, pump switches off and boiler shuts down.

Where do I start looking?

The thermostat or the motorised valve? Or could be somewhere else?
Can anyone point to simple to test of the motorised valve?

Many thanks, John.

 

[muggles]

Sounds like you need a new head for your motorised valve, but it could be the stat, best way of finding out is to break out the multimeter and do some electrical testing

 

[mysteryman]

It is probably the Synchron motor in the valve head. Moving and latching the lever into the manual position does not take the valve far enough to operate the end switch for central heating.

 

[BigJohnD]

I'll give the thermostat a test with the meter, and if it's OK which I expect it will be, I'll visit the local plumbing store for a new V4073A motor.

Many thanks,

 

[expertgasman]

I'll give the thermostat a test with the meter, and if it's OK which I expect it will be, I'll visit the local plumbing store for a new V4073A motor.

Many thanks,

test for 240v across the terminals (carefully!!!) to the synchron motor, with everything calling. If 240v is there, and valve not opening, you have your answer

 

[bengasman]

How did you override the clock?

 

[tonybhoy]

Link the orange and grey wires in the wiring centre with a heating demand and see if the boiler and pump starts if it does your motorised valve's micro switch is gubbed.

 

[mysteryman]

You'll get the same result if the motor's failed - which is more likely.

 

[BigJohnD]

How did you override the clock?

Put everything on constant!

I've not figured the wiring completely. They've used two parallel cables instead of multicore so it's confusing, and it's all unlabelled.

Wiring box

• BigJohnD
• 17 May 2011
• 1

There must a tidy electrician somewhere!

However with everything "ON", the white "Heating On" wire responds to the room stat, i.e. live when the temperature is set above the ambient temperature and not live when the temperature is lower.

There is no response from the motorised valve.

So I reckon that the motorised valve is shot. I read they're prone to failing from over-heating!

Untitled

• BigJohnD
• 17 May 2011
• 1

I've ordered a Honeywell Powerhead Replacement 40003916…

Cheers, John.

 

[Agile]

I think that we have been telling you the valve is faulty since you first posted here!

 

[BigJohnD]

I think that we have been telling you the valve is faulty since you first posted here!

Guess what? It's not working!

But thanks for bearing with me.

 

[bengasman]

How did you override the clock?

Put everything on constant!

That won't do much good if your timer is faulty.

 

[BigJohnD]

I fitted the new motor this morning and all is well.

I had to be a contortionist to access one of the retaining screws of the motor, lying on my back, with arms threaded through various gaps in the space by the bath and using a pocket mirror but with care and patience I got there.

The wiring, despite looking a right mess, was actually exactly as described on the wiring diagram of the valve fitting instructions.

It seemed to take an age for the system to fire up after completion and switching the electricity back on, but eventually it did, and it now behaves as it should, responding correctly to the clock and thermostat (Horstmann DRT2 Digital Programmable).

The back up batteries in the thermostat and timer retained the settings, but as the Duracells were all dated 2012, I decided to replace them with new ones dated 2017 and review/reset the on/off times and temperatures. I retired a few months ago and hadn't yet changed any of the settings to align to my new lifestyle!

Thanks to all for your support.