Radiators Hot when water only on

[Zingari]

Chaps

Can anyone assist as it is driving me mad. Over the summer despite having the theromostat low the radiators have been getting hot when I only want to heat the water!

I suspect the British Gas MV22M three-way value has something to do with it and is either knackered or the toggle switch is broken or in the wrong position. However with no markings for what the switch does in each position I am at a loss.

How can I test the valve or looking from above at the top of the valve with the switch on the top side what position is left and right supposed to be?

If the three-way valve is knackered can it be replaced without draining the system?

Heating system is the 'standard' set up with gundfus pump, lagged cylinder and header tank in the loft

Thanks

 

[gaspro1981]

Unclip the actuator from the valve body
Make sure the stem of the valve (brass unit) is free and operates freely from side to side
Operate the hot water and heating for a short period and confirm that the motor is driving the lever on the actuator from a to mid point to b And that lever returns back smoothly when heating is turned off
I think not 100% sure that the lever on on the actuator should be at rest on the letter b marked on the actuator for hot water only

 

[Armo74]

The valve is stuck in mid-position, you will have to remove the actuator with the power isolated and see if you can free the valve by gently turning the spindle from left to right. If it is seized then a drain down is the safest option if you are doing it yourself.

 

[Zingari]

Thanks. I take it then I take off the plastic body to teh valve to get to the actuator?

Also I have noticed that all the rads in the house get warm apart from one (upstairs bathroom) and having bled it there is no air only cold water it refuses to heat up. Both in/out rad pipes are also cold at the base. Could this be a factor?