Your Help Required - Heating coming on with DHW

[Ray1000]

Ideal Logic Heat System Boiler at my sons house.
Noticed radiators were hot when Nest timed hot water was called for.
Checked the three way valve the lever was slack
Couldn't hear or see any movement on the valve head when switching manually between CH & DHW.
Removed the Synchron motor and replaced it with an unknown spare.
At some point the lever had the proper action, but lost it later.
Still no apparent movement on the valve head when switching manually between CH & DHW
The motor that came off was distinctly hard to turn and had a burnt out smell to it.
The second hand replacement may be faulty but it does turn smoothly.

Q1. Should you be able to hear and see movement with the lid off when flicking between CH & DHW?
Q2. Can you tell by measuring the resistance across the two wires if a spare will work OK?
Q3. Can you simply test the Synchron by safely applying 240 volts - if it runs - it's OK?
Q4. Is it generally always the Synchron motor rather than the gearing to the valve that fails - which would call for a complete new head?
Q5. What is the best action to see instant movement on the valve ... CH on & off ... Water on & off ... CH & DHW together ... or flick between the two?

Thank you for your help
Ray

 

[BigSnoopy01]

Should motor when turning clock on and off on heating. Only time motors not working is when you have hot water only on and its warming up. Power off everything. Does the lever spring closed?

 

[Ray1000]

I'll have to try that when I go down to his house and let you know.

Re: Q3. In the meantime I powered up the old motor and it turned as it should, albeit still hard to turn by hand.

Q6. What other part could be stopping the valve going to DHW only

 

[CountryFan]

Q6. What other part could be stopping the valve going to DHW only

The spindle.