Myson MPE322 - Rest Position

[Irie]

We've got a bit of a problem with our Myson MPE322 - I think the actuator isn't working properly. If I've understood things right, the rest position when everything is off should be the DHW position? Ours is resting on CH and so there's no resistance on the manual override switch unless DHW is on. It reaches all positions fine, but rests at CH which seems wrong to me.

Does it sound like it's time for a new Actuator?

Thanks!

 

[flameport]

DHW is the default position, but there are circumstances which can result in it being at CH even though there is no demand for hot water or heating.

Does it return to the DHW position when power is disconnected from it? (meaning the entire heating system has no power at all, not just when the programmer etc. is set to off.)

 

[Irie]

Yes it does. However, once the power is back on it stays there until CH is called for. When neither CH or DHW is on and it's reading at CH the unit gets pretty warm there's a sight hum and it feels like a motor is running. Once it's in DHW position (either by manual turning or power off) it's silent and still.

 

[flameport]

That is all normal operation - with no power the valve is kept at DHW by a spring inside, when CH is selected power is applied and the motor inside moves the valve to either the mid position or CH only.

If the system is set to both DHW & CH OFF by the programmer and the valve is at the mid position or CH, this causes the motor to hold the valve at CH. This means the motor runs all the time and creates the hum and heats up. This continues until either DHW only is selected, or power is disconnected completely.

 

[Irie]

Brilliant thanks. So I guess if it's on dhw only then off it would stay in dhw position?

One final thing, one rad (the one next to the airing cupboard) heats up when only dhw is on, does this suggest the valve itself isn't closing rather than the actuator not working correctly?

 

[simond]

It could suggest a number of things, the two you have mentioned above, plus the installer not fitting the CH returns in the right place.

 

[TCCHeating]

One final thing, one rad (the one next to the airing cupboard) heats up when only dhw is on, does this suggest the valve itself isn't closing rather than the actuator not working correctly?

Just a thought.

Is the rad that gets hot with hot water only in the bathroom by any chance?

Gravity how water systems were often piped up so that the bathroom rad comes on with the water.

This was a good idea. Because it meant you could still dry a towel on the bathroom rad in the summer. But not so good if the system has since been converted from gravity into fully pumped.

 

[Irie]

Yes, it's in a bathroom nearest the hw tank. I guess that makes sense I will keep an eye and see how it all behaves, thanks!

I've noticed the boiler keeps cutting out (and then firing up again) which makes me think there's air somewhere after we had a powerflush done. Does this sound plausible? I will try and bleed everything and see if it all starts behaving!