If I have the right thermostat it comes in two parts sender with dial, and reciver seem to remember it is a square box with button and green and red LED.
I seem to remember they changed the frequancy so likely you will need to change both, although I would give it a try first at pairing, but the ST9400 should not need changing.
Adding to last reply you do realise this thermostat needs batteries? Pair of AA batteries are used.
Had same thermostat in last house, may seem old but in fact it is very good, it has fail safe, if the base does not see the thermostat in 30 minutes it auto switches off, and also has anti-hysteresis software, as it approaches target temperature it starts to switch off and on so it does not over shoot.
I personally like it cooler when I retire for the night, and some modulating gas boilers don't work to full efficiency when switched off/on so I wanted a programmable thermostat, thought I was being very cleaver using a programmable thermostat, however it went wrong and did not fail safe so room went to 32 deg C.
So returned to Honeywell as so much better quality, OK this house fitted Nest Gen 3, which is hard wired, as did not want to have to change batteries, but room temperature controlled by programmable TRV heads all Nest does it turn boiler off on a warm day.
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by ericmark » Fri Jan 31, 2020 9:38 pm 
by tomguest » Mon Nov 30, 2015 11:52 am
