room thermostat getting to warm

[ino58]

room thermostat
have i got a problem.i have my room thermostat set 16 c.
heating comes on in morning and just seems to keep getting
warmer.clock is set to go off at 8o.clock.everything turns off okay
but i have noticed if i turn thermostat up it does not click to come
on until the 20 c mark.surely this is not correct.have had new
wall thermostat since i noticed this problem.i think the problem
may have started when i had a thermostatic valve fitted.the guy
was fiddling with the wiring in the airing cupboard to do with the
valve.is there any possibility the wiring was not put back correctly
yours hopefully.

 

[ChrisR]

I don't follow you 100% but yes, it sounds like it's wired incorrectly.

 

[croydoncorgi]

Depending on the type of thermostat, you may be a wire short! Mains-voltage thermostats in many cases REQUIRE a nutral connection as well as a switched -live. If it is this type and there are only connections to Live, Switched-live and earth, the thermostat will not work correctly.

But from your description, it sounds like it's not connected at all - a 4 degree temperature difference with the temperature still increasing suggests that the thermostat is not doing anything at all. Wiring sequence should be as follows:
- from programmer CH-on to room thermostat Live
- thermostat Switched-live to Zone valve (usually brown wire)
- ZV Switched Live (orange wire) to boiler & pump.

If you have a 3-port valve instead of (a) two-port Zone valve(s), the colours and connections will be different but the sequence Programmer - Thermostat - Motorised valve should be the same.

If you find that the thermostat is the problem, with no neutral connected, be very careful! First of all, if there are only 3 wires available and already connected (live, switched live, earth) DO NOT use the earth wire. If the thermostat designer didn't want his box earthed he would not have provided an Earth terminal! Also, some boiler use low-voltage controls. If so, connecting mains neutral to the thermostat is a Very Bad Idea. Quickest and cheapest solution would probably be a digital thermostat with 'dry-contact' switching (battery-driven models only require two wires), or a 'Combistat', which can handle mains or low voltage and does not require a separate neutral connection.

 

[ino58]

had man round to look at problem.said everything seemed to
be working okay.but did not look at wiring?.he said he thought
it could just be the room thermostat that is faulty and suggested
it may be worthwhile upgrading to a digital room thermostat
which i agreed to.just wondered if anybody could give me there
views as to whether this could rectify the problem and if these
digital thermostats are a lot better than ordinary thermostats
thanks for all your help