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Just for clarity, let me highlight the relevant part of the post: TBH I'm getting fed up with it all and would prefer to replace the Sunvic with something else. Can anyone recommend a reliable alternative 3 port MOMO valve, or have any other suggestions? Like have Sunvic produced a more...

I think I have got something referred to elsewhere as a fairly common problem with these actuators, in that there ae sometimes failures on the HW side. Here is an outline of the problem: HW works on demand every time. If CH is demanded while HW is being demanded valve goes to mid position...

I am suffering the same problem. I have just replaced an SDM 1901 actuator for a replacement - and it already has the same problem. Can anyone advise me of a replacement 3 valve actuator. Or failing that a reliable alternative make that will just drop into this system. Many Thanks

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...

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?

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...

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...

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.) :lol: 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...

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...

Thanks - looking at it now.

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?

I'll go check when I confirm that the motor actually turns the valve. May take a little while, but thanks for the steer. :)

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...

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...

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...