Here is an explanation how a mid position valve works. The Sunvic is slightly different, but the principle is the same.
http://content.honeywell.com/uk/homes/FAQ/v4073aop.pdf
CH problem
- Thread starter ESL
- Start date
Here is an explanation how a mid position valve works. The Sunvic is slightly different, but the principle is the same.
http://content.honeywell.com/uk/homes/FAQ/v4073aop.pdf
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Thanks for that. Looks interesting.
I'll get poking around tomorrow when I get back from work. (Not a CH specialist, as you may have gathered.)
The thing that sort of confuses me is sometimes the CH will get hot, but only when the system needs to heat HW as well - of course when the tank stat reaches it's set point, that's it off.
But more often than not, the place is bloody freezing. I guess it's looking like the actuator or the micro switches inside it. Luckily the Sunvic actuator is an easy replacement without doing any plumbing. Electricals I can manage.
I'll get poking around tomorrow when I get back from work. (Not a CH specialist, as you may have gathered.)
The thing that sort of confuses me is sometimes the CH will get hot, but only when the system needs to heat HW as well - of course when the tank stat reaches it's set point, that's it off.
But more often than not, the place is bloody freezing. I guess it's looking like the actuator or the micro switches inside it. Luckily the Sunvic actuator is an easy replacement without doing any plumbing. Electricals I can manage.
When the call is for both HW and CH then water is fed to both sides, but only till one of them gets satisfied, then the non satisfied side gets the full amount. The side to get satisfied first is almost certainly the HW side as it's not in constant use and insulated whereas the CH side is losing heat through the radiators fairly quickly.
If you run off some hot water the call for HW will most likely bring the valve to mid position and you will get CH as well for a short period and this is what makes it confusing.
No doubt a replacement head will solve your problem.
It solved my problem and I've since cleaned the contacts of the microswitch and that now works ok so don't throw the old head away.
If you run off some hot water the call for HW will most likely bring the valve to mid position and you will get CH as well for a short period and this is what makes it confusing.
No doubt a replacement head will solve your problem.
It solved my problem and I've since cleaned the contacts of the microswitch and that now works ok so don't throw the old head away.
If you run off some hot water the call for HW will most likely bring the valve to mid position and you will get CH as well for a short period and this is what makes it confusing.
No doubt a replacement head will solve your problem.
It solved my problem and I've since cleaned the contacts of the microswitch and that now works ok so don't throw the old head away.
That seems to tally with my experiences to date, and I understand how it could come about. I'm still not entirely convinced that the call for CH is getting through, cos I don't see the actuator responding to the room stat, independent of the demand for HW, but I hope to bottom that one out tonight.
Have I got this right: If the programmer is within it's "ON" time for CH - The room stat signals a demand for heat, which is passed to the valve actuator which motors the valve to the relevant port and a switch in the actuator triggers the boiler? So it's the valve actuator that triggers the boiler - not the programmer or the room or tank stats?
I might as well take a chance on a new actuator and see what happens. It will be cheaper than any alternative I can think of.
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Nearly right, 5 out of 10!
When only the HW cylinder is calling for heat, the valve does not enter into it. The thermostat on the HW cylinder switches the power straight to the boiler.
But when CH enters the fray, the power to the boiler is via microswitches in the valve. The crafty thing is the way the valve can be held in the midposition so both CH and HW ports are open. Honeywell's solution is in the post I gave you. I don't know how Sunvic do it; they don't reveal their solution.
If you look at the wiring diagram and read the explanation, you should be able to work out which wire(s) should be live and when
Careful chaps, this is a Motor Open Motor Close valve which Sunvic have made to work with the standard wiring. So it should be the "Unishare" wiring on the Sunvic link, and not the MoMo wiring they show there as their "Minival" sytem.
So some of the comments in this thread about the valve "springing back" may well not apply.
Do check the wiring very carefully before you go buying a new head. A huge percentage of the STANDARD sytems I see are wrongly wired. With an unusual valve introduced, I wouldn't be at all surprised that it's wrong. Grey being live all the time, even when there's a demand for HW, is wrong.
So some of the comments in this thread about the valve "springing back" may well not apply.
Do check the wiring very carefully before you go buying a new head. A huge percentage of the STANDARD sytems I see are wrongly wired. With an unusual valve introduced, I wouldn't be at all surprised that it's wrong. Grey being live all the time, even when there's a demand for HW, is wrong.
Well I can vouch for that - it's not a spring return valve. The Sunvic valve is a MOMO type and can free rotate 350 degrees and has to be put into the correct operating position by the actuator. As far as I can see, the actuator only ever rotates the valve in one direction to divert the flow.
(BUT I don't know if it is meant to rotate both ways and is therefore faulty.)
Its not clear on the valve body which way to position the valve to allow flow to both ports, or if there are two positions (180 degrees apart) I just did it by touch to get both ports equally hot with the boiler running. This gives me CH as long as there is a demand for HW, which is keeping the house tolerably warm until I can get this fixed.
Cheers.
(BUT I don't know if it is meant to rotate both ways and is therefore faulty.)
Its not clear on the valve body which way to position the valve to allow flow to both ports, or if there are two positions (180 degrees apart) I just did it by touch to get both ports equally hot with the boiler running. This gives me CH as long as there is a demand for HW, which is keeping the house tolerably warm until I can get this fixed.
Cheers.
Sorry but I'm being a bit of plank tonight!
Grey live all of the time = wrong. This seems to indicate either a fault or a wiring error. Which wiring scheme should be in use please?
Just been looking at the sunvic site and your valve is a straight replacement for quite a few 'spring return' valves without any change to the wiring. The diagrams shown also support this.
So CH on programmer feeds room stat, then switched live from room stat feeds 'white wire' of actuator.
HW ON on programmer feeds cylinder stat which has two output terminals. One to boiler/pump (not satisfied)and one to 'grey wire of actuator(satisfied).
HW OFF on programmer also feeds the 'grey wire' on actuator.
The 'blue wire' is nuetral as you know and the sunvic diagram does not show any green earth wire.
On a spring return valve when HW only is called for and it has not yet been satisfied the 'grey wire' cannot be live. It only becomes live when HW is satisfied or HW turned off. If HW is being demanded, then valve can not go beyond the midposition because it needs a live grey wire to do so.
So CH on programmer feeds room stat, then switched live from room stat feeds 'white wire' of actuator.
HW ON on programmer feeds cylinder stat which has two output terminals. One to boiler/pump (not satisfied)and one to 'grey wire of actuator(satisfied).
HW OFF on programmer also feeds the 'grey wire' on actuator.
The 'blue wire' is nuetral as you know and the sunvic diagram does not show any green earth wire.
On a spring return valve when HW only is called for and it has not yet been satisfied the 'grey wire' cannot be live. It only becomes live when HW is satisfied or HW turned off. If HW is being demanded, then valve can not go beyond the midposition because it needs a live grey wire to do so.
Thanks for that. I'll have a look at it tonight when I'm finished work.
Many thanks for all your pointers chaps. I'm sure I'm getting closer. I would be quicker but can only work on this some evenings. Still - the weekend is nearly here and I want it fixed by Sunday!
So does the missus...
Many thanks for all your pointers chaps. I'm sure I'm getting closer. I would be quicker but can only work on this some evenings. Still - the weekend is nearly here and I want it fixed by Sunday!
So does the missus...
If anyone wants to know how the Sunvic MOMO valve works, it's all explained in their Patent Application here:
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=IE20030706&F=0
If you think the Honeywell spring return valve is complicated, wait till you read the patent.
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=IE20030706&F=0
If you think the Honeywell spring return valve is complicated, wait till you read the patent.
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