Another Motorised Valve / Cold Rad Problem?

[Illmatic]

Ok reckon I've got this now. In order for the CH to heat up properly, there has to be power on grey wire. Achieved by power from one of the two blue wires, either because HW isn't on or HW is satisfied.

This definitely happens when I turn off the HW, and also when I turn the stat right down. My thought is maybe with the stat at its normal operating setting, it is not reaching a satisfied state, and so not putting power to the grey wire. This would point to (as newgas said) a faulty cylinder stat?

I will do some more tests tonight, and check the pipe temperature either side of the valve as you suggest, to confirm the valve is moving. I think its ok though, as I can get CH on its own.

Thanks for sticking with me - really appreciate it.

 

[Homesafe]

i changed cylinder stat. on a system that had same fault and it sorted prob.

£20 approx. for new stat. 15 mins. to change.

if not take it back

 

[D_Hailsham]

1. CH only = all rads hot
That's correct.

2. HW only = water hot, upstairs rads warm, downstairs cold
The rads should not be getting hot, which suggests that either the valve is leaking to the CH circuit or there is reverse circulation somewhere.

3. CH & HW = water hot, upstairs rads hot, downstairs cold
Says the system is not balanced properly.

 

[Illmatic]

newgas, thanks for this advice it does seem a sensible way to go, as at the very least it eliminates the stat as a problem. Interesting to hear you've seen the same problem. As you say, can always return it....

Regarding the balancing, I did think this originally, and tried turning all the upstairs rads off, but still got no heat into the downstairs when the CH & HW were on together. That and the fact that all rads get nicely hot when CH is on only made me think it wasn't a balancing problem. Do you agree?

 

[Illmatic]

Quick question -

At the moment HW only is on, boiler ran for a time then stopped, but there is still no power on the blue wire from the stat to the grey wire on the valve.

So this means the stat is not satisfied, but why has the boiler stopped running? Shouldn't it keep heating till stat is satisfied?

 

[MANDATE]

I would say the stat is satisfied , it's turned the boiler off (unless the boiler stat is set very low) but power is not coming out of stats 'satisfied' teminal. Most likely due the contacts being dirty/burnt.
I had something similar in a 3 port valve, nothing coming out of the orange wire to fire boiler. I eventually stripped microswitch down after verifying fault to find burnt contacts

 

[Illmatic]

Does it send a signal to the boiler on a different wire then, to tell it to turn off?
Anyway, tonight I have left the hot water on at the programmer along with the CH, but with the cylinder stat turned down to 40. The rads have all been hot all evening and the house is roasting!

I think I will get a new stat on saturday and see how that works.

I will report back over the weekend.

Many thanks all.

 

[MANDATE]

Does it send a signal to the boiler on a different wire then, to tell it to turn off?

No. There are only two sources of power to light the boiler, each having a switch incorporated somewhere which turns it off.
On the HW side the switch is the closing and opening of the contacts in the cylinder stat when the temperature is reached. But as I said it's a two way,so it breaks one set of contacts and makes the other set, so the power gets diverted in order to move the valve onward from mid position (thats if it is in mid position)
On the CH side the switch is the closing and opening of the contacts in the room stat. This time its just a one way switch so power is just cut, it does not get diverted.
The room stat provides power to the valves white wire to (a) move the valve to mid position. At this stage it depends if HW has also been selected and wether or not it satisfied.
If HW has been selected and its not satisfied then the valve stays at mid position (until either HW or CH is satisfied)
If HW is not selected then the valve moves on to CH only. How? because HW is OFF the 'grey' is live and that not only drives the valve to CH only it holds it there against a stop. Also because the cylinder stat is not in use, the valve has to supply the power out through the orange wire to light boiler. It does this through a microswitch which is triggered as the valve travels beyond the mid position.
When the room stat is satisfied, it cuts off the power to white and the boiler stops. But the micro switch remains closed and valve remains at the CH only position, just waiting for the room stat to kick in again.
This is what happens at night, if CH is the last to be turned off the valve stays energised all night until its turned on again and the room stat switches boiler on

 

[Illmatic]

Ah I understand!
So the 2 way stat switch could be breaking contacts to switch off the boiler, but not making contacts to power the grey wire and move the valve.
Cheers for the explanation, you have been and are a great help.

 

[MANDATE]

Ah I understand!
So the 2 way stat switch could be breaking contacts to switch off the boiler, but not making contacts to power the grey wire and move the valve.
Cheers for the explanation, you have been and are a great help.

You've got it!

 

[Illmatic]

Just a quick line to report a success!
I changed the cylinder stat this weekend, and now have hot heating and hot water at the same time!

Thank you so much to all who contirbuted to this thread, especially MANDATE and newgas. Not only have I fixed my heating problem, I've also learnt a bit.

I will certainly be recommending this forum to anyone with DIY troubles.

Thanks again.