Evohome - poor temperature regulation

[G4RHL]

Interesting you should say that - we have just bought a car with the start/stop system and the first thing hubby said was 'switch it off as it will wear the ignition (or whatever???) out'. There needs to more information generally - almost like a selling point of these 'new' functions that will quash these immediate thoughts that people will have.

Incidentally, yesterday afternoon I noticed for the first time the boiler came on for a short amount of time when no radiators were calling for heat. It will have happened before but it was noticeable as I was sat outside in the sun I went inside to check and all them temps were way over the setpoints.

My car has the automatic switch off at lights etc. it works very well, I have had it 5 years and no problems. The starter motors are more robust to cater for it. If husband has doubts then tell him in my five years of ownership I have spent 34 hours stationary at lights etc. saving petrol. That is 34 hours when the engine would have been running burning fuel. I never reset the onboard computer from the day I bought the car, hence knowing how long.

As for inbuilt strength for so constant switch in of boilers I m not so sure, in November mine will be 18 years old. In that time we have had to replace the fan twice and that is £300 a time. The fan wears with constant on/off. Like you I also have heard the boiler come on for a short time despite every zone being way above set tempersture. It also happened yesterday, we had a warm day yesterday, no need for the heating to come on but it fired and having checked no zone was asking or needed heat.

If I go back to optimisation then I know I will have more frequent short cycles which do not seem to do anything plus I will have to change the set points so that optimisation comes on when I want the heating to come on and not an hour before. It would also switch off too soon as well such that we would have to put the heating back on. I suppose not now, it's 11C outside, clear blue sky and temperatures are rising - got the loos to clean before I can enjoy it though!

[G4RHL]

Once Evohome or Hometronic reaches equilibrium it will short cycle your boiler (usually 2mins per 10mins, but can be even shorter, say 30secs). If optimisation is OFF your system will spend less time at equilibrium, therefore less short cycling. As the weather warms, the system will reach equilibrium more quickly and you will notice more short cycling again.

But I have optimistion off and Evohome maintains my heating at equilibrium without any hassle, it comes on for a short time now and then to keep the tempersture constant and it always is but it does not come on as often as when optimisation is on. So what am I missing? I cannot think Honeywell would build in optimsation unless it was to achieve something. Currently in my case I remain unconvinced particularly as it comes on nearly an hour before the set point but it only takes 40 minutes to heat up to that point. Indeed a room is comfortable and quite useable within 10 minutes of it coming on.

[JohnnyP]

I hesitated over using the word "equilibrium", it's too subjective. In my earlier post, you could more accurately substitute "the state in which Hometronic/Evohome decides to short cycle". But that sounds a bit circular... From experience, the system reaches this irritating state when all the zones are stable near their setpoints and the heat loss from the zones is on the low side. It is possible for the system to be stable with all zones near setpoints, but not to have triggered the short cycling because of heat loss characteristics from the zones.

[G4RHL]

Just an update. Now many weeks since optimisation was switched off and no issues. All works as it should, temperature is kept balanced, occasionally but not often the boiler fires up for less than a minute and goes off. All works as it should. Yes, there could be some improvements but ones that ought to be capable of being addressed by software changes, but that apart, this is an excellent system. It just works.

[HenGus]

Just an update. Now many weeks since optimisation was switched off and no issues. All works as it should, temperature is kept balanced, occasionally but not often the boiler fires up for less than a minute and goes off. All works as it should. Yes, there could be some improvements but ones that ought to be capable of being addressed by software changes, but that apart, this is an excellent system. It just works.

Glad to hear it. Software changes.......? Perhaps all is not lost. We had a power failure in the night, and I came down to find that my £177 7 year old Evoke 3 radio needed a software update that was released late last month. The software update was via a Windows download and an A - B USB cable which was hidden away at the bottom of a drawer.

[Mavis]

Just an update. Now many weeks since optimisation was switched off and no issues. All works as it should, temperature is kept balanced, occasionally but not often the boiler fires up for less than a minute and goes off. All works as it should. Yes, there could be some improvements but ones that ought to be capable of being addressed by software changes, but that apart, this is an excellent system. It just works.

I am swaying towards switching my start up optimisation off as it is still, in the morning, coming on a whole hour before the setpoint and it only has to rise about 3 degrees. But I do like the optimisation off. Last night it kicked in the whole hour before the heating was due to 'go off' and the sitting room did not feel noticeably cooler. (Generally it has been kicking in around 45 to 30 minutes before.)

[paulockenden]

Reading through the whole thread, some people seem to think that the Evohome controller is directly opening and closing their radiator valves.

As I understand it, all it does is pass a target temperature to the valves. It's local 'intelligence' in the valves that decide whether and when to open or close.

P.

[G4RHL]

Reading through the whole thread, some people seem to think that the Evohome controller is directly opening and closing their radiator valves.

As I understand it, all it does is pass a target temperature to the valves. It's local 'intelligence' in the valves that decide whether and when to open or close.


P.

Plus the Controller is instructing "when" and telling the valve whether to operate having regard to pre selected conditions. A little more than simply sending it a temperature.

[willcurrie]

Better documentation should be available which explains the functional flow of the system. This would save people from having to guess, assume and interpret what happens in an evohome system.

[paulockenden]

Plus the Controller is instructing "when" and telling the valve whether to operate having regard to pre selected conditions. A little more than simply sending it a temperature.

Really? As I understood it it simply gets a new setpoint from the controller and then, completely autonomously, tries to achieve that. Are you saying there's more to it than that?

The reason I raised it is because someone said the controller should display which zone is calling for heat. If my understanding is correct the controller doesn't actually know this. But maybe I'm wrong.

Perhaps @Rameses could advise?

P.

[erik]

The controller has to know which zone is calling for heat, because the controller controls the boiler relay. It doesn't mean the controller decides when to ask for heat (the valve decides that), but the controlelr should certainly know which zone is asking for heat.

[paulockenden]

Ahh - I wondered whether a bound TRV and a bound boiler relay could talk to each other directly.

I suppose it would be easy to find out - pull the batteries from the controller and see if things continue to operate!

Even if the TRVs are calling for heat via the controller it could just be as a mesh type network (relaying commands without actually looking at them).

Who know.... Come on @Rameses, give us the details!

P.

[sharpener]

Ahh - I wondered whether a bound TRV and a bound boiler relay could talk to each other directly.

No, AFAIK you cannot do this, they are bound to the controller (or another central device e.g. a smart thermostat) but not to each other.

I suppose it would be easy to find out - pull the batteries from the controller and see if things continue to operate!

If the batteries are removed then comms with the valves will be lost and the system ceases to work (except for the BDR91 if the Failsafe mode is enabled). The valves also go into a fallback mode where they check for updates progressively less frequently and may take up to 24 hours to recover unless re-initialised manually.

Anyway the setpoints would not change according to the schedule as the time/temperature info is definitely stored in the controller.

Even if the TRVs are calling for heat via the controller it could just be as a mesh type network (relaying commands without actually looking at them).

AFAIK it's a radial network. If it were a mesh then intemediate nodes could act as range extenders by relaying messages, this does not happen in practice (but the facility has been requested by several people).

[SensibleHeatUK]

Ahh - I wondered whether a bound TRV and a bound boiler relay could talk to each other directly.

I suppose it would be easy to find out - pull the batteries from the controller and see if things continue to operate!

Even if the TRVs are calling for heat via the controller it could just be as a mesh type network (relaying commands without actually looking at them).

Who know.... Come on @Rameses, give us the details!

P.

The BDR91 (and the HC60NG before it) have 4 address slots which are used to register the communication links between paired devices, so that is why the Evo Touch collates the demannds from the HR92 zones and then sends a single demand to the BDR (thereby using one of the 4 address slots in the BDR). This is the same adressing method that has been used for all devices that have used the HR80 and HR92 (so Hometronic, CM Zone etc).

The system still uses a distriubuted intelligence model, where the control processing is genreally handled locally by that device, using comms between modules to pass relevent data (setpoint data from the main controlled, room sensor values from remote sensors, heat demand back to main controller or BDR directly in the case of HCC80R Manifold Controllers for example). That is how the system can then utilise the various failure modes to try and keep some basic form of operaion if one or more communication links drop out for any length of time (which varies depending on which device is in failure mode and what type of comms failure has occurrred).

[paulockenden]

So going back to my original point, is the controller just sending the TRV a setpoint, or as @G4RHL says, is there more to it than that?

P.