Strange regular 2C over setpoint temp reading on Kitchen HR92

[killa47]

I keep getting a regular 23C temperature read on the kitchen HR92 when the setpoint temp is 21C. Wondering if the reading is being skewed because the radiator is a 2 metre tall vertical type?

Any suggestions please as to why the normal 1.5C tolerance above setpoint doesn't kick in.

I know I could simply input a -2C offset to fix it but would be interested if the accomplished forum genii (latin) have any ideas as to what causes this phenomena.


Thanks.

[DBMandrake]

I keep getting a regular 23C temperature read on the kitchen HR92 when the setpoint temp is 21C. Wondering if the reading is being skewed because the radiator is a 2 metre tall vertical type?

Any suggestions please as to why the normal 1.5C tolerance above setpoint doesn't kick in.

I know I could simply input a -2C offset to fix it but would be interested if the accomplished forum genii (latin) have any ideas as to what causes this phenomena.

It's not quite clear what you're saying is wrong. Are you comparing the measured temperature on the HR92 to another independent room thermometer and the HR92 is reading 2C higher than the thermometer ?

Or are you saying that the set point is 21C but the HR92/Controller sometimes reports measured temperature as going up to 23C ?

If the latter, then I don't necessarily see anything unusual - cooking heat in a kitchen that was already being maintained at the set point by the radiator can easily lead to the room going over temperature due to the time it takes for the HR92 to react and turn the radiator off when cooking begins, then the time it takes for the radiator to actually cool down. And depending on conditions even with the radiator off the kitchen may still go over temperature due to cooking heat - as it often does in our kitchen.

Perhaps you can clarify what the issue is.

[killa47]

Or are you saying that the set point is 21C but the HR92/Controller sometimes reports measured temperature as going up to 23C ?

Yes, the HR92 is set to display measured temperature. These temps show during the daytime, often when my wife is at work - and I don't do any cooking at all in the day.

The kitchen is in an open plan setting with the conservatory, and the radiator is just inside the kitchen area. The conservatory shares an open wall with the snug, so there are three rooms in the configuration.

I know the real temperature could rise when the sun hits the conservatory windows but the 23C reading can appear when it's cold outside and no sun.

I have observed this for several months and been scratching my head. I thought I had exhausted all possibilities.

I could switch the HR92 to another radiator to see if it repeats elsewhere.

One other possibility is that I think the radiator valve body might be a Pegler Terrier rather than Honeywell Valencia and I know from two other radiators not on the Evohome system that these valves may be suspect because the non-Evohome connected valves are stuck open. Maybe the kitchen valve has started its death throes!

[Stevedh]

what %age does the controller show for demand for this HR92 when this is happening ?

[killa47]

what %age does the controller show for demand for this HR92 when this is happening ?

Apologies for late response due to weekend arrangements.

Just checked again this morning with TRV showing 23C. Controller shows demand of 9%. HR92 shows valve position is 0. Kept checking for several minutes. Then TRV went up to 23.5C so checked controller which showed it had then reduced demand to 2%.

I would have expected controller/HR92 to have dropped to 0% demand/valve position given the HR92 was 2C above setpoint of 21C.

Confusing but maybe the hysteresis stops it dropping to 0% demand?

EDit later. Just checked 10 minutes later and demand is now showing 0% so maybe the hysteresis function has too much time delay?
And later again showing 23.5C but controller shows demand at 15%.

[DBMandrake]

Apologies for late response due to weekend arrangements.

Just checked again this morning with TRV showing 23C. Controller shows demand of 9%. HR92 shows valve position is 0. Kept checking for several minutes. Then TRV went up to 23.5C so checked controller which showed it had then reduced demand to 2%.

I would have expected controller/HR92 to have dropped to 0% demand/valve position given the HR92 was 2C above setpoint of 21C.

Are you definitely checking the heat demand for the zone, not the overall system demand ?

And do you definitely only have one HR92 bound in that zone ?

Here is the relationship you should see between the HR92 reported valve pin position (option 10 in the HR92 menu) and the heat demand reported in the system summary page on the controller for that zone:

Confusing but maybe the hysteresis stops it dropping to 0% demand?

EDit later. Just checked 10 minutes later and demand is now showing 0% so maybe the hysteresis function has too much time delay?
And later again showing 23.5C but controller shows demand at 15%.

There's no hysteresis in the heat demand that I'm aware of. In my testing it always follows the graph above.

If you adjust the set point directly on the HR92 an updated heat demand is sent to the controller within a few seconds after the valve pin motor stops turning and will be displayed on the heat demand screen on the controller within about another 10 seconds.

So you could try adjusting the set point in half degree steps near the measured room temperature then wait about 20 seconds to see what heat demand is registered on the controller then compare that to the valve pin position and the graph above.

As to the cause of your problem - have you tried rebooting the HR92 by removing it's batteries and refitting them ? There have been a few reports on the forum of HR92's that work perfectly in all other regards but stop reporting the correct heat demand to the controller. I've had it happen to my bathroom HR92 once where it simply wouldn't call for heat from the controller even when I manually adjusted the set point between very low and very high. Rebooting the HR92 fixed it and it hasn't done it since. So give that a try if you haven't already.

If that doesn't help and the heat demand refuses to update with the set point there may be a comms problem. Do you still see the issue if you bring the controller into the same room as the affected HR92 ?

[killa47]

Thanks DBMandrake for a comprehensive response, as always.

I will check out your various suggestions tomorrow when can experiment some more.

I did have the Kitchen/Conservatory originally set up as a single zone with two HR92s and, after observing the 2.5C differential temperatures, switched the configuration to a multi room zone - with the Kitchen HR92 reporting to the controller. Didn't make any difference to the temperature variations.

Will report back ASAP.

[killa47]

Further to DBMandrake's detailed graph and explanation, I did re-check the HR92 valve position which when showing 46%, the corresponding demand at the controller was 11% - perfectly matching the graph per DBMandrake.

I am beginning to think the 2.5C differential looks to appear most frequently when there is an uplift in setpoint demand (often after I've put in temporary changes in other rooms which tends to bring on more consistent boiler firing). As the Kitchen HR92 is at the nearest radiator in normal daytime running (no demand from upstairs rooms), I wonder if simply the columnar radiator just acts a bit like a heat sump and pulls in a faster uplift of heat before the HR92/controller have time to respond.

The above is my best guestimate of what might be happening. Will keep monitoring in case it's of use to others.