Ariston boiler with Honeywell thermostat/timer

[Dazed & Confused]

Thank you for taking the time to read this.
We have recently moved into a new house which has an Ariston Clas HE system evo boiler (without clock) operated by a Honeywell ST9400C timing control with separate walled mounted thermostat.
Each of the three items appear to be operating correctly, however, somehow the timing control does not appear to be controlling the boiler ie the timing control switches on/off and does not seem to control the boiler, which appears to be constantly on. On the boiler we have both the water and heating set to on, with the auto setting engaged.
Does anyone have experience of this? I am hoping we have just got one of the settings wrong somehow.

 

[stem]

You don't show the full picture of the boiler controls. Usually there is a timeswitch included. Item 10 below.

If you do have the timeswitch fitted you now have two devices installed trying to do the same thing. The Boiler Timeswitch and the Honeywell Programmer. So, the timeswitch is usually taken out of service and the remote programmer can then take exclusive control.

Depending upon how the system is wired, that usually involves either setting the boiler timeswitch to be permanently 'on' 24/7 or sometimes permanently 'off' 24/7. Try both and see what happens, the Honeywell programmer should then control the boiler according to the demand for HW or CH. Assuming of course that it is wired in correctly.

 

[Dazed & Confused]

Thanks for the fast response, Stem, appreciated. Have attached another pic, but there is no number 10 timeswitch, it appears to be one of the models without it.
So, from what you’ve said it sounds like I need to change from the ‘auto’ setting on the boiler and try it being permantly on or off and see which works based on the way it has been wired.
Thank you, will try this and let you know if it works.

 

[JonathanM]

Thanks for the fast response, Stem, appreciated. Have attached another pic, but there is no number 10 timeswitch, it appears to be one of the models without it.
So, from what you’ve said it sounds like I need to change from the ‘auto’ setting on the boiler and try it being permantly on or off and see which works based on the way it has been wired.
Thank you, will try this and let you know if it works.

I think Auto might be something different, to do with setting the temperature.

Do you have at least one motorised zone valve?

 

[Dazed & Confused]

Thanks Jonathan.

Hmmm, no idea TBH. How do I check? I have a feeling based on how the heating appears to be working then maybe there are two; ground floor and first floor…?

 

[CBW]

Thanks Jonathan.

Hmmm, no idea TBH. How do I check? I have a feeling based on how the heating appears to be working then maybe there are two; ground floor and first floor…?

How many thermostats do you have? I take it you have checked the time periods on the Honeywell?

 

[JonathanM]

Thanks Jonathan.

Hmmm, no idea TBH. How do I check? I have a feeling based on how the heating appears to be working then maybe there are two; ground floor and first floor…?

Often zone valves will stick open or on, and the heating will keep running, even when all the controls are showing that it should be off.

 

[Dazed & Confused]

How many thermostats do you have? I take it you have checked the time periods on the Honeywell?

As far as I know only one thermostat on the ground floor. Albeit, the first floor has been running hotter than the ground floor, which I imagine could just be settings.
It seems less that the valve may be sticking open and more that the machines are not talking to each other ie one (Honeywell) saying off whilst the other one (boiler) is on.

 

[Dazed & Confused]

How many thermostats do you have? I take it you have checked the time periods on the Honeywell?

As far as I know only one thermostat on the ground floor. Albeit, the first floor has been running hotter than the ground floor, which I imagine could just be settings.
Yes, the Honeywell time periods are set up and appear to be working correctly, it just doesn’t appear to be communicating to the boiler / the boiler reflecting what Honeywell is saying it should be doing.

 

[JonathanM]

It seems less that the valve may be sticking open and more that the machines are not talking to each other ie one (Honeywell) saying off whilst the other one (boiler) is on.

What makes you think that? I'm not a plumber. But I have had at least ten occasions where the boiler has kept running when all the clocks are off. On every occasion it has been a problem with a zone valve.

 

[CBW]

If you only have one thermostat, then you only have one zone. It might have been bypassed somewhere. If you feel confident - isolate the electric, remove the Honeywell programmer and post a photo of the wiring. It could also be bypassed at the boiler, but I’m not suggesting you remove the cover.

 

[stem]

How it works, is that when the timeswitch and thermostat are both 'on' they are wired to a motorised valve. When the valve winds open it operates a microswitch inside the valve, and it's this microswitch that starts and stops the boiler as the valve opens and closes.

It's very common for a microswitch to stick. When that happens, the motorised valve will close and turn the radiators off giving the impression that everything is working as it should, yet the switch is still on and the boiler continues to run.

 

[Dazed & Confused]

Understood, thanks. Will try changing the settings and see if that works, and if not it seems like it could be a valve sticking.
Thanks all