Any ideas re Frost Thermostat

[Jim]

My programmer is calling for central heating but it wont fire. I get hot water ok. Discovered that if I meddle with the frost thermostat and raise it to about 7 degrees, the boiler will fire up the central heating. Its not satisfactory as I want the programmable thermostat to do the job. Any ideas about problem/solution please. Its a Glowworm swiftflow 100 boiler.
Jim

 

[namsag]

Sounds like problem is with your programmable stat is it wireless and not communicating

 

[Jim]

No, it is a wired one . Honeywell CM 907 less than a year old. The boiler and frost thermostat are in the garage(cold place) and the programmable thermostat is in the hall.

 

[Garfeild]

Zone/mid pos valve not moving over?

 

[D_Hailsham]

My programmer is calling for central heating but it wont fire. I get hot water ok. Discovered that if I meddle with the frost thermostat and raise it to about 7 degrees, the boiler will fire up the central heating.

The frost stat should turn the boiler on when the temperature drops to the figure set on the dial. If it's set to 5 degrees and the boiler does not come on, but it will when the dial is set to 7 degrees, then the temperature is not dropping as low as 5 degrees.

That's fine, but the frost stat should not prevent the main stat from controlling the boiler. The only way I can see this happening is if the two stats are in series, rather than in parallel. The other thing you should have is a pipe stat, which works in conjunction with the frost stat. This turns the boiler off when the water temperature reaches 15-20 degrees.

[code:1]
F= Frost
M= Main
P=Pipe
F M
Series Supply ________/ ________/ _______Boiler

M
__________/ ______________
Parallel Supply__/ \______Boiler
\__________/ _____/ _______/
F P
[/code:1]

The frost and pipe stats protect the boiler and prevents it freezing up. The night set back on the main temperature protects the house and prevents it getting too cold.

 

[Jim]

Problem seems solved.
For info,some time ago my room thermostat(mechanical) was replaced by a programmable one. This superseded the timer incorporated in the boiler. A few days ago I had an electrical outage which my plumber says affected the timer on the boiler (even though it is no longer used). It meant the programmable thermo was nullified and not controlling the boiler.He eventually pressed the reset button on the old timer and everything works now. Apparently the old timer was set to auto & run and left connected up. The new programmable thermostat in the hall takes over the boiler timer function. I hope this makes sense so that it might prove helpful to someone.
Jim