DIY Doctor

Thermostat Replacement

Postby Mike Dybacz » Mon Feb 11, 2008 12:29 pm

I have a combi boiler which used a Honeywell rotary thermostat. I have just replaced the thermostat, as its broke, with a digital Sunvic TLX 7501. The Honeywell had 5 connections but used only 3 i.e. 1 3 and 4 and the TLX 7501 has 3 connections 1 2 3. I have got the thermostat working i.e. switching the central heating on, by connecting 1 to 3 and 3 to 2 but it does not seem to switch off when the correct temperature is reached.
Anyone got any idea as to why ?
Mike Dybacz
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Simply Build It

Postby ericmark » Mon Feb 11, 2008 4:34 pm

In general old thermostats had live in, live out, neutral, and earth. The new ones run on battery and are double insulated so only have live in and live out. But also may have normally open contact as well as normally closed. The normally open will not normally be used. There are normally instructions saying which is which with each unit. Often there is a delay built in.

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