3 way motorised valve problem on CH

[boy01zone]

I have been having problems with the hot water getting "very hot" and cylinder stat having little effect on this.
I've now changed the motorised part of the honeywell valve, but this seems to have little effect.

Is it best to change the Brass fitting as I understand the rubber ball inside can stick?

Exactly how do these 3 way mid position valves work?????

 

[John506]

3 port valve has 3 ports.

A - Central heating
B - Domestic hot water
AB - Flow from boiler.

There is a ball in the middle of these ports, if you choose to have CH on, but don't wish to have hot water from your tap, the ball will move and cover the B side, so the water can flow from AB to A.

If you wish to have hot water from the tap but CH off, it will move and cover the A side, so water can go from AB to B.

The reason it is called a "mid position" is because the ball can also sit in the centre of the valve, letting water from AB into both A and B, so you can have Central heating on and get hot water at the same time.

The other version called a diverter valve, cannot sit in the "mid position" to supply both, only one at a time.

Your domestic will have priority though, so if you turn your CH on and run a hot tap, your CH won't heat up until you turn the tap off. But this doesn't apply to you as you have a mid position and it can supply both.

I wouldn't think it would be the 3 port valve preventing your water getting very hot, probably dodgy control thermostat.

 

[boy01zone]

If I turn only the hot water on, and adjust the cylinder stat should I see the motorised valve open and close? As currently if I turn the stat up I can see the valve open but when I turn it down the valve doesn't close. Its a new valve atenuator.
Can it be the brass fitting,i.e. the ball not working or what?

 

[John506]

If you want to replace the valve, take off the cover and just renew the motor.

 

[boy01zone]

If you want to replace the valve, take off the cover and just renew the motor.

Its a complete new motorised valve the bit on top of the brass fitting, I haven't changed the brass fitting, I've noticed that the spindle is not too easy to move, requires pliers, should the spindle move freely?

 

[John506]

It can be a bit stiff but no way should need pliers.

Isolate power
Drain system
Disconnect wiring
Open compression nuts either side
Remove valve
Remove nuts and olives from new valve
Place valve onto old compression nuts
Re wire as it was
Fill system
Turn on power

Voila.

 

[John506]

To change just the motor, take the cover off, there is a screw holding the motor in place, remove this and motor, cut wires, use connectors to connect the new motor to the wires, screw motor in place, cover back on.

isolate first

 

[boy01zone]

thanks for your advice, buying a new brass fitting tomorrow

 

[matt1e]

If I turn only the hot water on, and adjust the cylinder stat should I see the motorised valve open and close? As currently if I turn the stat up I can see the valve open but when I turn it down the valve doesn't close. Its a new valve atenuator.
Can it be the brass fitting,i.e. the ball not working or what?

No, the valve plays no part in hot water only, the only time it will move on hotwater only is if CH has just been on previously in which case it will return from either mid position or the heating position to the hot water position
from then on turning the cylinder stat up and down should fire/turn off the boiler only
if your hot water is getting too hot on hotwater only then its nothing to do with the valve (persuming you have a correctly installed Y-plan)
its the cylinder stat I would be checking

Matt