Honeywell room stat

Discussion in 'Engineers' Talk' started by Tulipa, Apr 29, 2022.

  1. Tulipa

    Tulipa New Member

    Hello, I'm looking for some advice on room thermostats. I have a wired mechanical Honeywell stat. I'm wondering what is a normal temperature drop before heating comes on. In my case it's 2.5-3 degrees. So if I set stat to 20, heating won't kick in until temperature drops to 17.5 or so. The thermostat is close to a radiator but not above it and heats up to just under set temperature. Do all mechanical thermostats work like this? It seems too big of a gap to me.
    Thank you.
     
  2. Hausfix

    Hausfix Screwfix Select

    I think 3 degrees is considered a fairly normal tolerance with mechanical room stats..Never done it myself, but you’ll be able to take off the cover and adjust the calibration by means of an adjustment screw by the electrical contacts.
    Personally, I’d swap it for a digital stat as they are still pretty cheap but you get the advantage of knowing exactly what temperature the stat is reading and it will activate as soon as the temperature dips just below the set target.
     
  3. Tulipa

    Tulipa New Member

    Agree that would be better option. I am a DIY novice and am not sure how difficult it is to swap a mechanical one for a digital one. Do you connect the wires and its ready to go? I have a condensing combi Ariston e combi evo. Would any digital stat work with it? Would you say it's cheaper to maintain a steady temperature in the house or heat it up for an hour or so and than cool down for three?
     
  4. banger

    banger New Member

  5. Teki

    Teki Screwfix Select

    Modern thermostats/boilers regulate the temperature intelligently so you don't have on/off cycles.

    If you are looking for more precise control, use a digital thermostat. If you want App/Internet then consider a smart thermostat like Nest, Hive or Tado.

    If you aren't sure about the wiring, switch off the power to the boiler/thermostat, remove the thermostat cover and take a photo of the wiring and post on here.

    As @banger mentioned, you may be better off with a remote thermostat as the current position may not be optimal.
     
  6. Tulipa

    Tulipa New Member

    Hello, hope you are having a nice Bank Holiday weekend (rainy one over here). Thank you for your advice. Was considering Honeywell t3 wired prog. thermostat with fuzzy logic. But then I read a post somewhere else where somebody said they had to get rid off theirs as it kept firing the boiler every 1 to 2 minutes to keep temperature on 18 degrees. That is exactly what I'm afraid of so now I'm put off :(.
     
  7. MGW

    MGW Screwfix Select

    A mechanical thermostat often has a heater inside which reduces the hysteresis. For it to work it needs a neutral.

    However as said modern gas boilers are designed to modulate, I.e. turn down rather than off.

    Two methods, one is a thermostat connected to the ebus common OpenTherm you clearly don't have this.

    The other method is with TRV (thermostatic radiator valve) which as it turns down the flow which in turn forces the by-pass valve to open, which allows hot water to return to boiler, which turns down the boiler output.

    However there is a problem, using water temperature it can't turn the boiler on and off once the water stops circulating, so it needs a method to stop the boiler cycling when weather warms up.

    The mechanical thermostat without the neutral connected works well to do this, if fitted in a room normally kept cool, hall for example, so TRV set to 17 degs C and wall thermostat to 18 degs C once it does turn off it stays off for a good time, but in winter it never turns off.

    The problem is a mechanical TRV does not have 17 degs C but *123456 which is a bit useless.
     
  8. Teki

    Teki Screwfix Select

    The T3 intelligently adapts to keep the room at a stable temperature. In the first few weeks of installation, it may seem like it's switching the boiler on and off frequently. After a while, this should settle down once it knows when and how long to fire the boiler to reach your set temperature at the desired time.

    If you still find it is firing too often, there is a cycle rate option in the installers menu which you can reduce. This value is the number of times the boiler fires per hour.
     

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