New thermostat learning shenanigans? Honeywell T3R

[JayN]

About two months ago I replaced old hysteresis type thermostat with T3R, which obviously is not smart but as I understand it, it can take two weeks or so for the stat to settle down (it learns something?)

I've programmed certain temps for certain times of day, evening one is an interesting one. Comes on at 6.30pm for 19 deg and goes to 15deg at 9.30. Thermostat is in the living room, normal sized, two largish radiators. One door is closed so the heat stays in. For some time now the temp has only reached to 17.5. Two radiators in the living room are proper hot but others only nicely warm (just the way I like it). But 19 is not reached, temp stays at 17.5.

So I cranked it up to 20 temporarily, and in 15minutes or less temp was at 20, 2.5deg increase. I could feel the heat on my face, another thermometer confirmed the 20 degrees. Now also other radiators are warmer.

So my question is, why was the temp holding at 17.5 when set at 19, but at 20 setting it very quickly climbed to 20?

I started to get worried my radiators are undersized to reach 19 in 2-3 hours but it looks like that is not the case - the increase in temp was very noticeable.

Cheers

 

[JayN]

Same thing this morning, temp set to 20, stays at 17.5. Pump it up to 21 and it actually goes to 21. So why does it stay at 17.5, what's the difference? And why 17.5?

Boiler is set to 70 and the stat is in the livingroom.

Thermo dynamics and physics is hard!

 

[MNW67]

It could just be overshoot. There is a proportional zone on these thermostats, set to 1.5C by default. So if thermostat is set at 19C, then when it gets to 17.5C the thermostat stops the boiler operating continuously and starts instead to run it in very short burst in order to slowly inch its way towards the 19C target. When you increased it to 20C, the boiler would have come out of the proportional zone and gone back to firing continuously. A lot of heat would suddenly be produced which might have been enough to take it up to 20C.

Once it gets to 20C does it maintain that temperature or does it drop back down.

My Auntie has a different Honeywell thermostat but it works in the same way and she has similar confusing issues.

 

[JayN]

Thank you! That must be it, it does do short burst, which I mentioned in my other post when installed the new stat as I was a bit baffled because with the old stat it wasn't doing that.

When it gets to 20deg it seems to ease off a bit, perhaps it doing 18.5 then.

I agree with your Auntie, it's very confusing. It's just that I've set it to 19 or whatever I expect to see 19. What I would like to have is a digital stat with plenty of programmable periods and no smart thinking, good old hysteresis.

 

[MNW67]

What I would like to have is a digital stat with plenty of programmable periods and no smart thinking, good old hysteresis.

EPH Combi Pack 4 used to have a choice of hysteresis or TPI (which is the method Honeywell uses). I haven't checked recently to see if it still does that, though.

 

[MNW67]

The TPI algorithm will probably give much better temperature control than hysteresis. There is an option on the Honeywell ones to set a minimum boiler ON time. I did notice, though, that you have extended the anti cycle settings on the boiler so I don't know how that will all interact.

On the EPH CP4 you could actually adjust the amount of hysteresis so in theory that should make it more sensitive, but I have never had one myself.