Sunvic SDM 1901

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 and everything works.

However, once HW is no longer being demanded CH does not always kick in. I may need to raise and lower the wall thermostat several times or toggle the CH on and off at the controller before the CH will kick in. Eventually the actuator may fail and CH only never works.

I have had this problem before and have recently changed the acuator for a new "old stock" one I found on the old interweb. But now the replacement is doing the same thing - so it is obviously a common fault.

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 reliable alternative model?

Many thanks

George

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 reliable alternative model?

I know how to fix it, i want to ditch it and replace it with something that works reliably please.

You don't say what size of valve you are trying to procure. There are many light commercial options.

Alternatively just remove the MOMO and fit a Honeywell spring return if it is a domestic sized unit. Changing the wiring is simple.

Copied from another thread just to clarify issues here - the modern Sunvic valves can easily be repaired.

As a scientist/engineer I mend quite a few of these as a hobby since first publishing my SeeRed webpages on Sunvic valves. The link is given above or just ask Google for SeeRed website + sunvic valves.

There are basically two types of domestic motorised valves - MoMo (motor on and motor off). These are in my view the best type if only because of the uniform motor torque available throughout the whole range of travel.

TWO PORT spring return use full motor voltage to stay in the open position and get warm, they eventually fail but often just because of an easily fixed microswitch problem. THREE PORT (mid position) use full motor voltage when fully open (central heat only) and reduced voltage (via diode and a resistor) when in mid position. These fail more often not because of motor failure but because at mid position full restore torque is not available and a sticky motor may not return reliably to the closed (dhw) position. Sunvic SD2701 and variants are notable here. They also have microswitch issues - again often easily fixed.

I am appalled by the number of actuators that are thrown away - when they can be mended for much less than the cost of a new actuator. This applies especially to the Sunvic MoMo design which is actually quite clever despite its design weakness, and is covered in my webpages. Sunvic 2301 and 2701 and variants are also thrown away in large numbers.

If any plumbers have a large box full of failed actuators I would be interested in obtaining these to see how many could be mended and to publicise this - as an aid to conservation and reducing waste.

Many householders pay over £100 to have an actuator replaced when often a £12 repair is all that is needed. Some installers replace programmers when it is just the motorised valve actuator that has an intermittent fault.