Evohome - large temperature overshoots

[garmcqui]

Hi all,

I installed Evohome to control my parents oil central heating a few weeks ago. Simple system - 12 zones, configured as one DHW relay and a boiler relay, hot water overrun set to 10mins. Boiler demand set to 3 per hour, minimum of 3 mins each time. Optimisation is turned off (for now). System is working fine, BDR91's turning on and off when they should etc, so no binding issues. Parents over the moon with it.

Now at the time it was installed there was no pump overrun. Believing this was wasteful, last weekend I had my dad install a simple overrun timer to keep the pump running for 10 mins after boiler demand finishes, which seems to work fine.

However, this week, the Evohome has been overshooting set temperatures more, often by 3 or even 4 degrees, making rooms uncomfortably warm sometimes. For example, living room set to 17C reaching 21C!

What could be causing this? Would the system benefit from a factory reset so it can "learn" with the pump overrun (if it does learn at all!).

Thanks,

Gareth

[top brake]

Remind us of what zones and how controlled?

[garmcqui]

Unsure what you mean mate?

All zones controlled by HR92's.

[top brake]

Unsure what you mean mate?

All zones controlled by HR92's.

Something very odd going on

Do the TRV fully close? Additional heat gains? Pictures please

[garmcqui]

Thanks for getting back.

Yes, all radiators HR92's fully close fine. There are no possible additional heat gains.

[top brake]

Thanks for getting back.

Yes, all radiators HR92's fully close fine. There are no possible additional heat gains.

Yep do a hard reset to force a re-learn

[garmcqui]

Ok, will take the batteries out for a while.

Do I have to reset the HR92's too? Do all the zones have to be rebound?

[top brake]

Ok, will take the batteries out for a while.

Do I have to reset the HR92's too? Do all the zones have to be rebound?

No

Just a reboot on the Evo controller.

Thanks

[f1arp72]

Hi all

Talking of temperature overshoots, can I get everyone's opinion with regards to how my system is currently working using NO Optimisation setting at present. Have been using system for about a few days now and have 21 as my setpoint all over my house. Last few mornings, the upstairs has not required heating but the 3 rads have come on downstairs, having required a boost from about 19 to 21. I presume with no optimisation set, the rads do not turn off until they hit 21 but my rooms then continues to heat up to 23.

Can it be correct that I can gain another 2 degrees from the time the rads (supposedly) turn off and the water cools in them ? Just seems a lot to me. (I must add, two rooms switch off, but third does continue to ask for heat as it's a conservatory and heats up slower. However, the rad in this room surely can't heat up the entire bottom floor of my house !!)

I will switch on optimisation at some point which I hope will turn off rad sooner knowing the room will continue to heat quickly up to 23 !! On that, are the HR92s CONTINUOUSLY learning or is there a period where they think they know it all !!

Thanks

[willcurrie]

I'm not using the optimisation as it doesn't suit my system. For the first few days I has some big overshoots but it soon settled down and now generally is spot on.

[f1arp72]

I'm not using the optimisation as it doesn't suit my system. For the first few days I has some big overshoots but it soon settled down and now generally is spot on.

Thanks. I hope my system does the same as I'm having massive trust issues with it at present. Came home tonight and my house is a bit on the toastie side. Heating is set to 21, but all zones (8 of them) were 21.5 and above. All rooms downstairs were 23 and it feels uncomfortable.

Seems there's a lot more effort to get this system working than I'd hoped. I guess I need to play around with Optimised Stop, Temperature Offset on the HR92s and maybe changing temperature to 20 instead of 21 (as a last resort).

I have thermometers in my rooms downstairs, and with the old fashioned heating system with standard thermostat set to 21 in hallway, all rooms seemed to maintain a nice 21. Now I just keep seeing them at 23.

I'm beginning to lose confidence with this kit which is a shame as it's taking all the fun out of having it installed and this whole kit cost me a lot of money (for me anyway)

[willcurrie]

I'd suggest setting your room targets a touch below your ideal then leave it to bed in for a few days. once it's settled down you can try some of the other settings. Change one thing and evaluate the change over a few days then move onto the next. You will be happy with your system in a few days once it's happy with your house.

[G4RHL]

I would not loose confidence. It works and it works well. Just make sure everything is all properly set. I switched off optimisation as there seemed to be little advantage to it, it was bringing heating on too early and often would short cycle. The system does work well.

[paulockenden]

All rooms downstairs were 23 and it feels uncomfortable.

Are the rads in radiator cabinets, or do they have furniture pushed up against them? Is there a free flow of (normal room) air around the HR92s?

If not you might be better off with a DT92 controlling the room temp rather than relying on the rad valves.

P.

[erik]

Optimisation as far as I know does not influence the precision of how a room is heated. It changes when the systems comes ON or goes OFF. But it shouldn't make a difference in precision.

@paul: I would expect the HR92's to heat too quickly when there's no free air flow, which would actually cause undershoots instead of overshoots.

@f1arp72: I hope leaving it running/learning for some time will fix it for you. I have personally tried Evohome 18 months (2 winters) and it has always continued to overshoot big time for me (only to cool down and then overshoot again). I have given up on it myself and am using a very simple cheap thermostat now, that keeps everything nicely around the desired temperature. However, there's other folks here who don't have these problems, so it might start working fine for you as well!