Apollo Myson Boiler shuts down when HW selected

[smiler84089]

Hello.
Many years ago the programmer and 3 way valve actuator were replaced by a plumber and i think since then whenever i select HW or HW & CH the 3 way valve actuator rotates until a click is heard and the boiler shuts down.
When I select CH only the valve actuator rotates and the boiler kicks into life and all is well in the house.
I have got away with this set up by shutting off the TRV's during summer and having the CH come on for 30 mins on a morning to get a tank of hot water however I wish to sell the house and I want to bottom out the fault and have CH, HW and CH & HW as options with the programmer.

I'm guessing that there exists a problem with the 3-way valve actuator wiring but when i have traced out the wiring and compared it to a wiring plan Y (best guess as to the actual set up) i see no obvious problems. I don't know whether I should shell out for another 3-way valve actuator and wire it in or whether i should check the wiring for perhaps a fault there causing the actuator to do the wrong action and wrongly shut down the boiler when it should kick into life (water cool and boiler cool).

Any advice is truly appreciated as I have fixed just about every other part of the system over the years (thermocouple, stats, new programmer, new fuse) and I want to solve this issue.

Cheers

 

[mysteryman]

You should check the wiring. Most five wire mid position valves use the same colour codes and wiring layout - there are others such as the obsolete Switchmasters, but these can be replaced by a five wire valve. Some rewiring is needed. As you can select CH only, you need to be sure that the DHW OFF and cylinder thermostat satisfied terminals are connected to the grey wire.

As this fault has been there since you had new kit fitted, you should check that the wiring is correct as the first step. Some installers and sparks do not in fact know how to do it.

Look at the Honeywell website.[/list]

 

[oilhead]

Sounds like possible fault with cylinder stat. What make is your 3 way valve and what timer do you have/