Boiler and Programmer light stays on even after OFF time

[jverdoes]

Hi all,

I had a problem with my Glow-Worm Fuelsaver F boiler that didn’t want to switch off. I checked the Honeywell L641A hot water cylinder thermostat and noticed that the small switch inside had seized. I immediately replaced the thermostat and wired it exactly as the old one.
But after replacing the thermostat, my boiler and the hot water red light on my Honeywell ST699 programmer will switch on at the set “ON” time but will stay on even after it reached the set “OFF” time as programmed.
Eventually, the boiler will stop but the red light will still remain lit.
The boiler thermostat dial is set between 4 & 5 and 55*C on the cylinder thermostat.
I read through many forums but got mixed solutions to the problem. Some say it could be the controller while some say the motorized valve is not closing. I don’t want to replace one of these only to find out that it was actually the other that caused the problem.
I would really appreciate any feedback on this.

Kind regards,
Johan

 

[D_Hailsham]

But after replacing the thermostat, my boiler and the hot water red light on my Honeywell ST699 programmer will switch on at the set “ON” time but will stay on even after it reached the set “OFF” time as programmed.

The red light on the programmer is controlled by the programmer. If the programmer goes off, the light should go off. Try disconnecting all connections form the programmer to the HW thermostat, then check what happens to the light. If it goes out when the programmer goes off you must have wired the cylinder stat up wrongly

Eventually, the boiler will stop

That's the boiler stat kicking in.

The boiler thermostat dial is set between 4 & 5 and 55*C on the cylinder thermostat.

55 is OK but 60 is better.

 

[jverdoes]

Hi D_Hailsham,

Thank you for your reply and advice.
I'm sorry that I wasted everyone's time, and mine, for I had a huge brain fart...
There is luckily nothing wrong with my system and the re-wiring is correct.
Bright Spark here set the timing on the programmer incorrectly...
I forgot that when you slide the selector to "ONCE" on the Honeywell ST699 programmer, it uses the 1st programme "ON" and the 2nd programme "OFF" to switch the system on or off.
The 1st programme "OFF" and the 2nd programme "ON" are then ignored.
My programmes were set at 05:00-06:00 and 20:00-21:00 therefore it came ON at 05:00 and OFF only at 21:00.
Oh well, at least I had sufficient hot water...

Thank you anyway...!