Intermittent CH pump operation. HW OK

[Richardah]

Recently, the CH pump has failed to start some mornings. If I switch on the HW the pump always starts with no problem. SO something is failing to tell the pump to switch on.

There is a 3-way Honeywell valve. When I remove the actuator head, the valve turns easily with finger pressure. I have fitted a new 40003916-003 replacement head, and thought that was the end of the problem, but it's just happened again.

After fiddling with the actuator (moving the lever up and down, and turning it on and off), the pump eventually started (and once it is started it keeps going).

I would be most grateful for any ideas

 

[twgas]

Sounds like you have a problem with either your wiring or CH controls.
How long have you had this problem?

 

[Richardah]

Thanks for getting back so quickly, Mick.

The problem started less than a week ago after years of operation.

The light on the control indicates that it's on, but perhaps it's lying?

Richard

 

[MANDATE]

There are three positions that the valve can be at.
(a) HW only
(b) HW/CH
(c) CH only.
When HW is involved in the selection, power from programmer HW ON goes to the cylinder stat, across the stat and feeds boiler/pump.
If the selection is (b) the room stat supplies power to drive valve to mid position so both ports are partly open, but it's still the cylinder stat that provides the power to operate boiler/pump.
When HW becomes satisfied the cylinder stat cuts out and the power divertered to the valves grey wire.
This drives valve over the second stage and triggers a micro switch which allows power out of the valves orange wire.
If (c) was selected without HW then white wire powers valve over first stage and grey takes over for second stage.
I'm guessing here! but I'm thinking that your valve is not moving through the second stage or if it is then there is no power coming from orange wire. It's not clear if valve moves over the first stage.
For the valve to move over stage 2, the valves grey wire has to be live, so where does the power come from?
Well if HW was on and becomes satisfied the cylinder stat diverts power to the grey. This is of no use of course if HW was not selected so to cater for this a wire from programmers HW OFF terminal is used.
The fact you have a new head would suggest the wiring relating to the feed to the grey wire from one or both the sources mentioned is most likely where the problem lays.
Could be something simple like loose connections or terminal screw on insulation.
Don't forget the orange from the valve joins the cylinder stat and it wiil be live when HW is on and can mislead you.
Two easy checks before you go too far.
With both HW and CH off the grey wire should have 240v (from programmer)
Wth CH on the white valve wire should have 240v (from room stat)

 

[Richardah]

Thanks Mandate - I'll check the voltages in the morning. I had wondered about a loose connection and tried waggling the wires in the junction box, but that did not make the system spring into life.

Richard

 

[Richardah]

Just to let you know that it came on OK this morning, so I can't make any useful measurements. I will do so the next time it plays up, and let you know how I get on.

Thanks

Richard

 

[Richardah]

Hi

Just to let you know that it didn't come on this morning, so I was able to check voltages. There are 0V on the white wire when the CH is on. The green light is on the wireless thermostat box indicating that it should be on. So I guess I need to look at that.

Richard

 

[Agile]

Now you tell us!

The RX unit usually has just two wires from its switched output and these are connected to the boiler ext. thermostat connections in a combi boiler or in place of the room stat in a wired system like yours.

So you need to measure for 240v between earth or neutral and each of the wires from this stat, obviously both should be live when its on.

Tony

 

[Richardah]

Hi Agile

Thanks for coming back so quickly. As you know, intermittent faults are a pain as you can't make any measurements when everything is working OK!

Anyway, the fault is in full swing. In the junction box there are 4 wires going to the wireless RX unit (Drayton Digistat SCR).

Red and blue 240 V on red

Black 240 V

White 0 V

Thanks again for all your help

Richard

 

[MANDATE]

The actuator head needs 230v on the white wire to move the valve to mid position. It then needs 230v on the grey if the valve is required to move from mid position to CH.
So it looks like the room stat is where the problem could be (loose connection or dirty contacts)
You need to check if room stat is receiving 230v and delivering 230v.
If it's not receiving 230v then problem could be further back at programmer

 

[Agile]

I would guess that the red and black are the supply to the RX unit.

The black has 230v and is from the programmer but the white has 0v and obviously the fault is in the RX unit as predicted ( eventually ).

Its usually a failed relay in that so replacement of the whole unit is the usual cure except for the dedicated electronics enthusiasts.

Tony

 

[Richardah]

Thanks very much for your swift replies. (I am dividing my time between troubleshooting and helping the family pack up after a visit)

Guess it has to be the receiver unit. I shall have a look inside when I have worked out how to take the cover off. (there is a screw at the bottom right corner. I have loosened this so the corner is no longer attached, but the front does not want to lift off)

Richard

 

[Richardah]

The stupid thing has started working again, so no more diagnostics until it stops!

Richard

 

[Richardah]

Except, of course, to verify that there is now 240 V on the white wire.

I am wondering about connecting the white wire directly to 240 V as I never use the thermostat but rely on the radiator stats?

Richard

 

[Richardah]

It's still working, but next time it fails I am very tempted just to connect the white wire of the Honeywell controller to the 240 V line - unless I hear howls of protest?

Richard