Problem with 3 port valve

After some advice please.

I had a new 3 port valve fitted in October 2023 after the previous one started playing up (not working for heating only)

Last week the valve started to intermittently not come on when called for heating only (works fine if water is on too)

Once water reaches temp and both are still on (so know it’s not the cylinder stat) the 3 port valve starts making a buzzing noise and heating (and pump) doesn’t come on

only way to get it to work for heating only is to turn off at mains and control. This then turns the pump on but very low so boiler doesn’t fire.
If I do this a few times I can eventually get the heating to come on on its own (and pump to run)
It then continues for the rest of the day (coming on and off as the room thermostat calls for so know it’s not the room stat either)

The plumber is going to replace the actuator bit as Honeywell have agreed to send a replacement but I am worried this will happen again and it’s something else as the valve was only in for 4 months

I am wondering if this is an electrical issue rather than an issue with the valve itself.
Your thoughts would be appreciated

I am not a plumber

But thinking of how these valves work, the motor, the switch and the wiring are all in the head, and (should) work even if the head is taken off the spindle. The water valve is just a brass casting with a couple of pipes and a rubber ball on a rotating spindle. IME the valve part only goes wrong if it leaks or the ball wears out. They commonly last 10 to 20 years.

So unless the spindle was jammed and refusing to let the motor turn the internal mechanism correctly, I don't see how it could cause your fault.

If you are handy, you can actually take the head off the valve and see if it works, and turn the valve spindle with a pair of pliers.

Changing the head is quite a simple job as it is not a water part so there is no draining or bunging needed, no need to turn the water off.

It seems unlikely that the new one would have the same fault as the old.

There may be incorrect wiring or faulty controls, especially if you had similar problems with the old valve. I do not have enough knowledge of how to diagnose or fault find that.