CH problem

[ESL]

A couple of years back, we had a new Brit Gas CH system fitted and at some time between then and now the CH does not seem to want to work.

We have a standard fully pumped system with hot water storage tank fitted. Programmable time set to weekday/weekend programmes - separate HW and CH. Sunvic SDMV2304 3 port motorised valve.

The problem is that since the summer, I can't seem to get the CH to come on independantly. The HW programme is working OK in that it comes on and goes off when demanded, but the room stat won't activate the system.

I had originally thought it was a fault with the room stat and replaced it with a generic B&Q one, but it still won't fire it up.

At the moment I have took of the valve motor an manually positioned the valve to get the house warm but would appreciate a few pointers.

By no way am I a CH expert, but I am a trained electronics technician and know my way round a circuit diagram and a multimeter. What I dont know is how the system should be wired and what voltages go where to activate the CH when its needed.

A simple circuit diagram of a standard CH/WH system should do it if anyone cam point me in the right direction...

Many thanks for reading this far.

George

 

[sambotc]

You've kind of answered the question yourself, if the motorised valve is manually open and it working, it would appear that either the valve body has seized or the motorised head is knackered.

Cheers Sam

 

[ESL]

Well... not quite. Perhaps I did not make myself clear in the first post, so I'll do it here.

The valve motor "motors" just fine and the valve itself rotates and operates freely.

The problem is that the programmer and valve does not respond to the room stat's demand for CH only.

If I demand HW only - it works.
If I demand CH only it wont.
If I demand CH and HW, 90% of the time I only get HW.

The 90% bit is mad I know, but there it is - sometimes it's OK, most of the time it's not.

 

[sambotc]

OK.

If you have taken the head off and managed to get the motor to turn using the controls? then the electrical side of the installation /call for heat is working ok?

Otherwise how did you test the correct operation of the motorised head itself?

Could it be that the motor is not able to turn the valve body?

HTH Sam

 

[hi-spec plumbing heating]

is the grey wire in your wiring box got power when calling for heat not hw.

 

[ESL]

Well, much as you said really. I took the valve motor off the valve body and manually set the programmer HW override. and it motored to the HW port.

(I determined the valve positios from looking at the positions of the flat on the plastic gear wheel on the motor drive.)

Then I turned everything off and the valve motored back to what looks like it's mid point. (Do I assume then that when everything is off, the valve sits in the mid position?)

Then I demanded HW via the room stat (with the CH pverride on) and zilch.

I moved the valve by hand and it seems not to be stiff, so at the moment, I have just manually positioned it so that both ports are open, with a slight bias toward the HW port so that I always get CH when HW is demanded. And then just let the radiator stats control the room temps (except the Living room, which does not have a rad stat).

Now you mention it, Im not absolutely 100% that the valve motor is "actually" rotating the valve, so I'll have to go back and check to prove this - but the motor does turn, and the valve does not seem over stiff.

Hope this helps.

 

[ESL]

is the grey wire in your wiring box got power when calling for heat not hw.

I'll go check when I confirm that the motor actually turns the valve.

May take a little while, but thanks for the steer.

 

[D_Hailsham]

You can find the wiring here:

http://www.sunvic.co.uk/documentation/Catalogue Low Res.pdf

It is the Sunvic book, but the valve wire colours are standard.

Note that the programmer needs a connection from the HW OFF as well as HW ON. The HW cylinder thermostat also needs a connection from the "satisfied" (NC) as well as the "call for heat" (NO) terminals

When HW only is on the mid position valve does nothing. The fact that you only have problems when CH is on, points to the valve actuator. You can get the actuator separately, part no SDM1901

 

[ESL]

is the grey wire in your wiring box got power when calling for heat not hw.

I'll go check when I confirm that the motor actually turns the valve.

May take a little while, but thanks for the steer.

Interestingly, the grey wire (from the terminal block up to the valve actuator) has 240V on it at all times, unless I isolate the supply. That can't be right can it?

 

[ESL]

You can find the wiring here:

http://www.sunvic.co.uk/documentation/Catalogue Low Res.pdf

It is the Sunvic book, but the valve wire colours are standard.

Note that the programmer needs a connection from the HW OFF as well as HW ON. The HW cylinder thermostat also needs a connection from the "satisfied" (NC) as well as the "call for heat" (NO) terminals

When HW only is on the mid position valve does nothing. The fact that you only have problems when CH is on, points to the valve actuator. You can get the actuator separately, part no SDM1901

Thanks - looking at it now.

 

[MANDATE]

First the grey wire has to be live, coming from the programmer HW OFF.
This wire provides the power to drive the motor which turns the quadrant from mid position onwards.
During this action a microswitch is triggered and makes the orange wire live which lights the boiler. In the other positions the boiler gets the power from the cylinder stat.
So the problem is most likely the microswitch (if the quadrant moves fully to the end). If it does not move to the end it could be either faulty motor or no power on the grey wire. Or stiff spindle.
Somewhere on this forum is a wiring diagram.

 

[MANDATE]

Try a search for the author 'curious' under plumbing and central heating'.

 

[ESL]

First the grey wire has to be live, coming from the programmer HW OFF.
This wire provides the power to drive the motor which turns the quadrant from mid position onwards.
During this action a microswitch is triggered and makes the orange wire live which lights the boiler. In the other positions the boiler gets the power from the cylinder stat.
So the problem is most likely the microswitch (if the quadrant moves fully to the end). If it does not move to the end it could be either faulty motor or no power on the grey wire. Or stiff spindle.
Somewhere on this forum is a wiring diagram.

This sounds like it's getting close to the problem. It's getting late now so I'm stopping to let the kids get to bed, but thanks to all who replied.

The actuator seems to have more than enough torque to shift the valve OK and the valve rotates freely by hand and with the actuator powering it. Incidentally it is a SUNVIC MOMO 3 port. So I guess there is a signal not getting from the valve actuator to the boiler to fire it.

Many thanks all - I'll never be an expert but I'm learning all the time.

 

[hi-spec plumbing heating]

if the grey live and the orange is not it's faulty.

 

[MANDATE]

The grey wire is fed from two sources (a) HW OFF terminal from programmer and also (b) the 'satisfied' terminal from the cylinder stat.
If you turn off your system when the valve is in the CH only positon (even though you may have selected both HW and CH) the valve stays put till you next turn it on and HW is included in the selection.
This is why there are so many problems with motors I believe.
As you have found to get the quadrant to move back you have to remove all power or of course you could just select HW