Honeywell ST6400C

[John McLaren]

Hi all, the other day I noticed that our Honeywell ST6400C was showing a red light for “heating” but the heating slider switch has been set to “off” for the last couple of months.
I cycled the heating slider switch across to “continuous” and back left to “off” and the red light went out.
Any ideas what could have caused this strange fault, or is it time for a new controller?

Many thanks all
John

 

[cross thread]

sometimes you get a slight back feed from the diverter valve that can cause this issue,I would wait to see if it’s a problem before spending

 

[John McLaren]

Thanks very much

I shouldn’t really complain. The system is 18 years old, although the boiler is fairly new.