I installed a FantiniCosmi last October and am quite happy with its performance, it has a settable differential of 0.3C to 2.0C, I have mine set to 0.3C, it, as expected switches off at the the SP temperature, when cold it switces in at the SP-0.3C BUT once the room is up to temperature it seems to switch in at 0.1C diff but the display then falls by another 0.1C, however, overall it gives excellent control at this differential with (once room up to temperature) a overshoot of 0.2C . There are two settings which is handy as I can use one as a setback temperature or whatever, the display is not backlit. (Also non TPI)
Are there any thermostats with a good range of user adjustable hysteresis?
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Many thanks for the helpful replies and suggestions. Plenty of food for thought in there. Ultimately, I think I might just leave things as they are for now and be my own manual hysteresis adjuster! Or more simply, I'll turn it on and off as needed. Perhaps I was just being lazy.
We don't use the heating a great deal anyhow as we tend to favour the woodburner.
To answer an earlier question - yes, environmental concerns are also a factor. We generally have the bare minimum of heat needed and wear lots of layers and thermals. It's amazing how used to it you get over the years, and also how horrendously hot and stuffy other houses can feel as a result!
Thanks again for the help
We don't use the heating a great deal anyhow as we tend to favour the woodburner.
To answer an earlier question - yes, environmental concerns are also a factor. We generally have the bare minimum of heat needed and wear lots of layers and thermals. It's amazing how used to it you get over the years, and also how horrendously hot and stuffy other houses can feel as a result!
Thanks again for the help
An older boiler, which can only be full on/ full off, has to have hysteresis in the thermostat, for reasonable efficiency and to avoid too much wear and tear.
More modern boilers can ramp down their output, modulate - so they are producing less heat as they near the desired water flow temperature. Even better is a compensated control system, where the boiler's control knows it is close to the desired room temperature, so it can reduce it's heat output. My own system, manages to accurately hold the room temperature within a fraction of a degree, and the near constant temperature in the pipes and radiators, means there is no creaking as the system expands and contracts.
How warm or cold you feel, depends on many factors entirely outside the control of your heating system. I am very tolerant of the house being cold, for several hours after rising from bed, I am likewise tolerant for several hours after having had a hot bath. Moving about, busy doing chores, I like the house cooler. Settled down for the evening, maybe watching TV, I feel the cold more.
Hi Harry
Sounds like we are quite similar. I really like a cold house in the morning. It seems the heat from being in bed stays with me for a while, plus I'm usually busy doing this and that. So the usual thing is to open the windows for a short while to let fresh air in, and get on with jobs.
I probably should have said before what my current system is... It's a Worcester Danesmoor 20/25 boiler and a Honeywell T6360B thermostat (I think! Need to double check).
Cheers
Sounds like we are quite similar. I really like a cold house in the morning. It seems the heat from being in bed stays with me for a while, plus I'm usually busy doing this and that. So the usual thing is to open the windows for a short while to let fresh air in, and get on with jobs.
I probably should have said before what my current system is... It's a Worcester Danesmoor 20/25 boiler and a Honeywell T6360B thermostat (I think! Need to double check).
Cheers
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That might be your answer, it's a mechanical stat. Take the front cover off, normally you should have three wires one of which is the neutral. Disconnect it, it is needed for the shunt accelerator which is necessary to keep the hysteresis small. There will be wide swings between ON and OFF. Personally I wouldn't do this. If there is no neutral, add one, that might change your opinion on how the system is working.
Well maybe, apart from that. I don't like wasting expensive heat, in the winter. The only window which is normally opened is the bathroom window, f. or a while, after a bath. In summer, I keep the windows closed in the day, to keep the heat and flies out - just the back door open, which has a fly screen, then open them when it's dark to recool the house.
On my DT90E from a cold start it would stop the boiler at 1.5° before set temperature, wait a bit, restart, stop at 1° from set temperature, wait a bit more and stop .5°from set temperature, then restart before stopping at set temperature. When correct temperature was met, it would run the boiler something like every 12 minutes for a few minutes to maintain the set temperature and it never went over more than .5 of a degree. I think that aspect is better than the Hive setup I now have but the Hive has other benefits, so on balance, I prefer the Hive.
Depending on your ability and qualifications - it is possible to rigajig variable hysteresis using two stats along with a latching relay wired into the control line, whereby the low set stat (demand) initiates heat on. And the high set stat (satisfied) resets the heating to off. More info if required.
That is why your thermostat must include some measure of hysteresis, and you are getting the swings in temperature. The only way to avoid it, is with a modern boiler, able to modulate, plus a modern control system, to tell it when to modulate and by exactly how much.
We had a DT90E and what I liked about it was that when the heating came on, to stop it overshooting, it went up to 1.5° below set temp, switched off for a short while, came back on until 1° from set temp, switch off, wait a while and went to 0.5° from set temp. If the room didn’t get to set temp from what was still coming out of the rads, it went to set temp. At set temp, it would fire the boiler up 6 times per hour while it was at set temp but not go over by more than 0.5°. That worked fine on our old non-modulating boiler as well as our new one. I swapped it out for a Hive setup but that thermostat is not as good as the DT90E but it has other benefits.
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The thing I hated about my DT90E was the very loud click every time it activated. The stat was in the hall and I could hear it click from the upstairs bedrooms. It was soon returned for a refund.
I have a very basic FantiniCosmi Roostat, non TPI, set to its lowest differential setting of 0.3C, it gives excellent control with only 0.2C max overshoot once up to temperature, for some reason or other even though it switches off at the SP temperature it switches back on at ~ 0.15C differential, it has 0.1C definition so switches in below 0.1C but before it reaches 0.2C which is fine by me but when it cuts off it won't cut in until I raise the differential by the (theroeticall correct) 0.3C, similarly, when it cuts in I have to lower the differential by 0.3C to make it cut out. Temperatures checked with digital thermometer.
Yes, that’s what I was thinking. The neutral connection to the thermostat is for that heater. If your thermostat has a neutral connection and you want more hysteresis, disconnect it from the thermostat. Might be too much or too little, but easy to try
Brian
Edit: Sorry, hadn’t spotted that this has already been suggested
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Just saw your thread having ordered a Google nest thermostat and waiting on arriving, I thought this was going to be all singing all dancing but upon reading up on it I noticed that the histeresis cannot be altered under the set at .5°. The thermostat I have at the moment there is nothing wrong with it and I just thought the Google nest would be more user-friendly, what I do like about my current one is that the hysteresis can be set to different settings, .25, .5, 1, 1.5 and 2, allowing for a more comfortable environment, or a longer gap in boiler firing cycles. My current thermostat is a Salus iT500 and was around £100 to buy six years ago, I think I am just going to keep this and return the Google nest.
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