Diagnosing 3 Port Valve

[Tom JE]

Hi All,

For a while now my heating has been coming on with the hot water, even when there is no demand either from room stat or heating program.

It's a Drayton 3 Port valve.

I thought at first the motorised valve was faulty so I unclipped the motor unit from the valve body and could see the motor moving into the correct positions relating to the required demand of heating and hot water.

The valve itself *seems* OK to though. I mean I can move it freely by hand and it's only 4 years old. Before I replace the valve I wanted to run a few things past you all;
- With the motor removed and the valve in the closed position, all 3 pipes attached to the get hot (I was expecting the heating pipe to be cold).
- With the motor removed and the valve fully open the hot water pipe is hot (I was expecting that to be cold).
- The valve spindle only turns a fraction of the 360 degrees - see attached photo. Is this correct?

Do these valves fail internally?

Thanks,

Tom

 

[ianmcd]

That valve doesnt turn 360 degrees it only moves very slightly

 

[RigidRaider]

If the design is the same as in my Honeywell 3-way valve, the flow is controlled by a black rubber ball on the end of an arm, which moves under motor power and opens or blocks the two ports or leaves them both open.

 

[ReganAndCarter]

Put it all back together. With the system cold, turn on hot water. If the pipe from the ch port (A) starts heating up, it's the valve. Simples!