DIY Doctor

Honeywell Thermostat

Postby marshy07 » Thu Jun 07, 2007 6:27 pm

We have been in our house 4 years, so its quite newish. The heating works fine apart from the fact that you can't have the rads semi warm. They are either red hot or cold. The thermostat clicks at 20 degrees if its below the rads go off, if higher eg 25 degrees they get warmer. Is this normal? or is the thermostat faulty???

PLease help
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Simply Build It

Postby DONFRAMAC » Thu Jun 07, 2007 10:22 pm

I had a Honeywell thermostat when my house had under-floor electric heating, and I neglected to update it when I had gas fired central heating installed;---- usual vented system, with panel radiators and indirect hot water cylinder. Some years later I renewed the thermostat, and discovered that the unit needed incorporates a small heater/resistor fitted just below the bi-metallic strip type of thermostat. The unit was otherwise a copy of the Honeywell, but made by Sunvic---- direct replacement, but designed for fast cycling, just like the simmerstats on a cooker. My local electrical factor firm were on the ball there!---- Works great!
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Postby sparx » Wed Jun 20, 2007 7:58 pm

Hi further to Donframacs valid comment, check if your thermostat wiring has a neutral wire as well as live in and sw.-live out,
the human body feels about 1.5deg C change in air temp. so if your stat takes 5 deg to change over then room will always be too hot or too cold,
ie rads hot /cold.
to cut down on this dead band (hysterisis curve) there is a small resister fitted in the stat but it needs a neutral connection to work.
By the way you do appreciate that no thermostat can adjust the surface temp. of your rads, that is set by the boilers internal stat. your room stat only gives on/off control not proportional!
You need to check with drawing inside cover of stat but I think term 2 should be N
regards SPARX
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