grant vortex pro external oil boiler problem

[Cocolula]

the above boiler starts up intermittently at night when the programmer is not calling for heat. I have changed the frost stat but this happens even when the weather is not significantly cold. the two zone valves do not open so eventually the boiler shuts down on overheat condition. what should I try next?

 

[Norcon]

What make of zone valves are fitted?

 

[Cocolula]

they are Drayton ZA5 valves

 

[Norcon]

Could be the end switches in the zone valve faulty.
If you had said danfoss then certainly a possibility. Disconnected the end switches on mine and replaced with solid state relays and no problems.

 

[Cocolula]

is this something that a keen day man could do and if so where do I get the parts
could you give me some details?
thanks

 

[snb]

Frost stat will activate when air temperature is below 5degrees. Causes overheat because pump not directly wired to boiler. Needs to be altered to have a pipe stat wired in series with frost stat so it only activates when pipes below 5degrees.

 

[Cocolula]

would you expect the zone valves to open when the frost stat is activated and the boiler starts up?