Honeywell Controls Fault?

Stiltz · Dec 16, 2022

Hello everyone!

Since the cold weather started I’ve noticed that the Programer (Honeywell ST9420C) isn’t working properly.
It doesn’t turn on/off in the auto pre set times in the C/H mode. It works correctly in the auto pre set times in the H/W mode. The C/H is effectively on constantly, turning on/off on the thermostat.
I have a Honeywell DTS92E1020 RF stat, I’m guessing it’s paired correctly with the programmer because it does turn the heating on/off when the temperature drops/rises or is adjusted.

Any ideas why the auto times in C/H mode aren’t having any effect?

Deleted member 120897 · Dec 19, 2022

Is it knocking off on the programmer but staying on?

EvilDrPorkChop · Dec 19, 2022

Turn the HW to off and then test it.

Common problem on these, for some reason they go that they cannot pull both relays in together whilst on at the same time.

Deleted member 120897 · Dec 19, 2022

EvilDrPorkChop said:
Turn the HW to off and then test it.

Common problem on these, for some reason they go that they cannot pull both relays in together whilst on at the same time.

I have similar the other way with my Myson mep2c, if I use the boost the heating for an hour, and the water is on, sometimes it’ll knock the heating off when the hot water goes off.

Stiltz · Dec 20, 2022

Hello everyone, thanks for getting back to me so quickly.

The heating was coming on if the temp in the house dropped below the temp set on the RF room stat. This was happening even if the programmer was in the AUTO (OFF) part of the days timer settings. Hope that makes sense!!

Since “resetting”/changing the times (only by 10 minutes here & there) on the C/H pre set daily on/off times, the problem has rectified!!
It seems like changing/resetting the times has rebooted the programmers C/H timer. Like the programmer didn’t log the previous set of installed times. That’s the only way I can explain the sudden change.

Anyway, worth remembering if there’s a similar problem with one of these or maybe any programmers. Try putting the times into the programmer again! Worked for me!!

Cheers, everyone 👍