CH won't work but HW does!

[mbb2006]

Can any one help? Please? I have a problem with my central heating system and i have searched through the archives but i still haven't fixed the problem.

My system:
Potterton Suprema HE boiler
Drayton thermostat
Horstmann centaurplus C27 programmer
3 port valve with a BGMVSP-23 actuator
BG Multi Head III pump


The problem:
I cannot run the CH on its own. HW is fine, and HW and CH is fine (but i am not convinced of this as i suspect that the HW side is running the boiler and pump).

The detail:
When my programmer is set to CH only the system does not work, i get no heating, the pump does not operate and the boiler does not come on (no lights at all including the power light), however, the thermostat 'clicks' (nothing actually happens though) and the programmer CH light is on.

In HW Only setting everything works (boiler lights up and pump runs).

I have checked the wiring for the thermostat and it appears to be ok, i tried to 'test' the thermostat by linking the Live and Call and then turning the system on - No difference still not working in CH mode.
I have checked the wiring for the actuator and while everything checks out the actuator did not move when i tested it (by selecting HW,CH and both from my programmer) off the valve. Could this be it? But if so would this stop the pump from running?
I thought it might be the programmer so bought a Drayton LP522 programmer but it made no difference.
The pump operates in HW mode so i guess i hope someone can tell me why the pump and boiler are not operating when in CH mode.

if there is anything else needed please ask as i am getting desperate as i am going away tomorrow!

cheers for any advice

 

[45yearsagasman]

Have you checked that the synchron motor is working and powering the valve over to the ch position? I suspect not. Have you unclipped the power head and checked the spindle is not seized?

 

[mbb2006]

Thank you for replying.
I have taken off the actuator and tbh the only way i could think of testing it was to turn the heating/water and combinations therein on and watching to see if the actuator moved...it didn't. So does this mean the actuator is U/S and if so would that stop the pump from running when in CH only mode? if yes then it looks like we may have a winner and i need to get an actuator pronto on a B/Holiday at 5pm!!

 

[matt1e]

It will most likely be the actuators end switch not making, either due to the valve body starting to seize up or the switch contacts failing

it wont be the sycron 45yearsgasman, you missed this bit mate

and HW and CH is fine

Matt

 

[mbb2006]

Oops also meant to say i moved the valve about 20 degrees, i understand that this is about normal? it moved using hand power only so if 20 degrees is normal then i think the valve is ok.

 

[matt1e]

I cannot run the CH on its own. HW is fine, and HW and CH is fine

I have taken off the actuator and tbh the only way i could think of testing it was to turn the heating/water and combinations therein on and watching to see if the actuator moved...it didn't.

mmmmmm

does the central heating heat up when hotwater only is selected? and dd you remember to turn up the room stat when testing

Matt

 

[mbb2006]

Matt,
if the contacts fail to make on the actuator, will that stop the pump from running?

Matt,
i will check the HW only setting and test the radiators. will reply to this one in a couple of mins


and... yes the thermostat is set at 30 (max) for test.

 

[matt1e]

Matt,
if the contacts fail to make on the actuator, will that stop the pump from running?

yes and the boiler too, but only in CH only mode, the end switch plays no part when hot water is in demand

 

[mbb2006]

it is taking a little while for the system to cool down a bit (it is hot because i was testing in the HW and CH mode and didnt turn it off because the wife was cold!).
While im waiting... is there any logic to central heating systems?? i do not know how you guys manage to work half these things out!

 

[mbb2006]

Matt that sounds VERY hopeful...If it is that then if im ever in your neck of the woods i will owe you a beer or two.

 

[mbb2006]

Matt,
yes the rads do get hot even if it is set to HW only, i have noticed that the actuator (and so the valve) is set in the Mid position so this would be expected? wouldn't it?

 

[mbb2006]

UPDATE

I got a Drayton MA1 complete with valve and actuator. Used the new actuator and wired into a JB so that it will be easier if i ever have to do this again. Turned it on to CH and.......

IT WORKS!!!!


Thanks to everyone who helped me diagnose this and sort it out.

 

[matt1e]

Matt,
yes the rads do get hot even if it is set to HW only, i have noticed that the actuator (and so the valve) is set in the Mid position so this would be expected? wouldn't it?

No mate it shouldn't, looks like the wiring is wrong

hotwater only = valve at rest in hot water position = boiler and pump controlled via cyl stat

hotwater and central heating = valve in mid position or fully open depending on cylinder stat position = boiler and pump controlled via cyl stat when hotwater in demand or roomstat via valve end switch if valve fully open

central heating only = valve fully open to heating position = boiler and pump controlled by roomstat via valve end switch

Matt