Synchron motor in 3-port valve

[Set Square]

My 3-port mid-position (Y-Plan) valve has been playing up for a while - the main symptom being over-hot domestic hot water.

I've now replaced the actuator, and all is well - but I did a few tests on the old one first by removing it from the wet part of the valve, but leaving it electrically connected to see what it did. Starting from total power off, I powered the system and set the programmer and room stat to call for CH - with HW off. If working normally, I would expect the actuator to take a few (maybe 20) seconds to motor to the CH position and switch on the boiler and pump. Rather than 20 seconds, it took it well over 20 *minutes* to do anything - and even then it struggled to get past the mid position (explaining why it has been over-heating the HW when supposed to be on CH only).

After replacing the actuator, I took the old one apart, removed the motor and tested it by powering it from a safe block. When power was applied, it would do maybe half a turn and then stop. A nudge would make it do another half a turn - but no way would it run continuously.

Is this a common symptom, and does anyone know what causes this sort of problem with the motor?

[Harry Bloomfield]

Set Square laid this down on his screen :

It sounds like either the motors bearings have gone sticky, windings have become shorted due to heat, or the rachet mechanism which ensures it starts running the right way has jammed. The motors are of the type used and almost identical to an old style electric clock motor.

While ever the valve has to be opened, the motor runs in cycles. It runs to move the valve to a position, where upon a microswitch opens and allows the valve to return under spring pressure, causing the motor to run again until the switch reopens- a constant cycle.

I very much doubt you could do anything worthwhile to repair it, though you can buy replacement motors for around £18. Should the microswitch fail, these are available from Maplins for a couple of pounds.

After doing regular battle with our actuator for 20 years, I have determined that it is heat from the actual water valve which causes the actuators demise. The lubrication dries out, making the actuator spindle stick and the spring unable to turn it and the motor overheats.

A few years ago I added a heat deflector between valve and actuator, just a plastic disk of about 8" diameter with a hole in the centre for spindle and the two mounting bolts. The actuator runs much cooler and is now much more reliable than without the deflector.

I now always keep a spare actuator ready to replace the one in use.

[Trevor smith]

I had this problem a few years ago, this type of motor has very little strenght and where they are situated is rather hot and I think this dries out the lubrication in the bearings and it cant handle this resistance. After replacing mine I sprayed the old motor with WD40 and I ran ok for a while then jammed up again.

Trevor Smith

[Set Square]

It seems to be something magnetic. With the lid off the motor, the little disc on the top of the shaft spins quite freely - in either direction. But as soon as power is applied, it gives a kick, rotates through part of one revolution and then stops suddenly - usually in the same place relative to the poles in the casing. Give it a nudge, and it will do another rev - it just won't continue to run unaided.

What is the ratchet to which you refer? If this a mechanical device, my motor doesn't seem to have one!

I think that having a spare actuator is a good idea - and I'd probably repair this one as a spare, except that I've already resolved that in the summer, I'll throw the whole thing away and install two 2-port valves in S-Plan configuration.

[Harry Bloomfield]

Set Square formulated on Saturday :

Sounds like shorted turns in one section of the motor. This is the common problem due to heat in the windings and I think why they later modified the design to include a wrap around heatsink.

Assuming it is a similar motor to a synchronous clock motor, then a clock motor can start and run either way. To ensure they run the correct way, a mechanical device (like a ratchet) has to be used to ensure they start up the correct way.

Probably their is something in the mechanics of the rest of the actuator which performs this function.

Thinking back to when I last had one apart, there was no rachet on the motor and the little brass gog drive was able to spin quite freely either way. It is the motor with a built in reduction gearbox (I think) and two mounting holes to fix it down sticking out from the base?

[Set Square]

It looks pretty much like

- except that the numbers printed round the casing are different, and my HAS3 actuator doesn't feature in ScrewFix's compatibility list.