Smart Heating Controls - My Experience with Honeywell Evohome - Part 2: More Technical Points

During lockdown in 2020 it seemed like a good idea to get better control of our heating. My focus was better comfort, but saving energy would also be good. We had Evohome installed in September 2020.

 

So, with the perspective of 3.5 years after installation (March 2024), how has the system performed?

 

This is part 2 of this review. I posted part 1 in January, targetting user experience and this Part 2 is focussed on more technical points.

 

Selection & Installation

• The Automatic Bypass Valve (ABV) allows all radiators to have Evohome TRVs. It is a short copper pipe and valve added close to the boiler to allow for pressure release when the last radiator turns off and allow time for the boiler to turn off).

Automatic Bypass Valve (ABV) installed just under the boiler.

 

Early installation issues fixed by the installer during September and October:

• A couple of the TRVs did not operate correctly to start with - not sure why (maybe sprocket not engaged with the valve on one?)
• Hot water tank thermostat incorrectly installed (it turns out that the recommended installer had so far installed just 6 Evohome systems and that ours was their first with a thermostat for the hot water tank) - this was also fixed in a couple of visits.
• We had a pre-existing wiring fault; this took more extensive diagnostic work and much head scratching from Mike the installation engineer. He stuck with it and found the cause; a broken cable core between hot water tank and boiler.  I laid in a replacement cable (floor boards up, hole in the ceiling, etc) and he connected the cable at each end.

Installation result:

• From the installation starting in mid-September and finishing at the end of October we had a stable system ready for winter:
• Without the existing wiring fault I would not have needed the installer to return more than a couple of times.
• There were gremlins with the system, over the September/October period, that I fixed myself (eg valves that lost their calibration/off position).
• I agreed with the installer a fair split in costs for the extra work that was not included in the fixed price (the broken cable core was our cost, the rest was theirs)

 

Lessons learned (more technical points)

• The Honeywell documentation is OK for a working system but very limited on fault diagnosis and resolution. There is limited 3rd party material available online. So, learn what you can when the installer is on site.
• Testing the system can be frustrating. The time lag from changing a temperature setting can be from a few seconds to a few minutes as the change ripples through from TRV to app (or app to TRV) and then to boiler. This has never been an issue in day to day operation, but means that testing can take a long time and needs much patience . I am sure that there were a number of times I suspected a fault, but waiting a little longer would have proven that everything was working (see above on knocked confidence).
• I would recommend having a simple test script - eg
1. start with central heating off.
2. Check all radiators cold
3. Turn all radiators to target temperatures above the actual room temperature (eg +2deg) using the app, so that all radiators should come on:
• Wait 20mins (this probably only needs to be 5mins, but you want to be certain that it is not a time lag issue)
• Check each TRV has the new target temperature reading
• Check each radiator is warming up
• If the TRV has the right target temperature but the radiator is cold you can check the actual demand on each TRV on 'system summary' on the handheld display (press 'settings' for a few seconds and you get the option to go to the 'configuration' menu).
4. Turn all radiators off from the app:
• Test as above, but this time you have to wait longer for the radiators to cool down.
• A test script is useful because:
• You quickly identify faults with high level of certainty.
• It helps in removing any gremlins early.
• If there is a fault you can be very specific with the installer on what is wrong and confidently replicate the issue when they visit and then test that the fix has worked.

 

Evohome Software - Deficiencies and Recommendations for Honeywell

While software is pretty easy to use it does have a few (minor) deficiencies/frustrations:

• I have not seen any software updates. In writing this piece I have googled this point and I see that there has been an 'application software' update (mine is v02.00.17.03 and a May 2023 posting on the manufacturer's website has v02.00.19.33 - see https://resideo.my.site.com/ensupport/s/article/How-to-check-the-firmware-on-the-evohome-WIFI-controller?language=en_US). There is very little written about what the update does, other than it 'works on heat pumps' and has 'smart weather features'. I had registered my e-mail address, but Honeywell did not bother to contact me to tell me about the update. Apparently the update should be automatic, but you can also send your MAC address to Honeywell (now Resideo) and they will update the firmware (I have just tried this and the webform kept crashing - I will keep trying in the coming days and update this article if I get a result)...

...so perhaps all that follows is now out of date with the new version of software!

• While programming a new schedule is reasonably simple, it is also a little fiddly. It is Perhaps hard to see how to make it less fiddly on the Evohome controller with such a small display. Perhaps there is a case for a PC / iPad version of the software with a simpler drag and drop scheduling interface (there is a web interface - this seems like a simplified version of the hand controller and does not include a schedule editor)
• The handset and phone apps have different interfaces. Not sure why Honeywell went to the effort of developing 2 interfaces and putting all of their users to the added effort.

Hand controller scheduling interface	Hand controller temperature override interface
iPhone scheduling interface	iPhone temperature override interface

• The 'System Summary' screen is pretty useful in diagnosing issues - showing the %age demand on each radiator; it seems odd that it is buried on the configuration menu.
• I have not tried the 'optimum start' and 'optimum stop' features.
• I do think that these are a great idea  - Evohome learns the warm up / cool down profile of your home/room and you schedule the time at target temperature as opposed to the heating off/on times. In other words Evohome turns the heating on early on a cold winter's day so that when you get up the house is warm; on warmer days the heating comes on later saving you money.
• So why not use them? Given the initial 'teething problems' this seemed just another layer of complexity to go wrong; I wanted to build confidence in a stable system. I must admit that during the last couple of years I have pretty much forgotten about Evohome (which is what I wanted) and I have not got around to trying this feature. Writing this has got me interested again (I feel an experiment and another blog post coming).

 

After all the above 'negative points' I reiterate the point from part 1: The Evohome software is easy to use and fine for day to day operation. However, I do think that Honeywell has missed an opportunity and a few extra software features that would improve the value of the system:

• Self guided fault diagnostics / resolution (eg my low cost HP printer has great animations for replacing ink cartridges and all the faults that I have encountered over several years)
• Build in more fault tolerance (eg a monthly automatic TRV calibrate cycle and a proper battery warning on the hot water thermostat would probably eliminate >90% of the issues that I have seen)
• Better controls on going out / turning the heating off/down (Eco mode):
• Resolution of <days><hours><minutes> on when to switch the heating back on
• Include the option of hot water off and a check box to have this on, say, 24hours before the heating is on (I have the hot water scheduled just once per day and want to return from holiday with hot water in the tank)
• Checkbox option for 'optimum start' so that Evohome works out when to put the heating on for my expected return time, even if I am not using optimum start at other times.
• I see that other systems have 'geofencing', so that your mobile phone instructs the system when to turn on based on your phone's location. I have not used such a system, but my view is that this feature would be bad:
• My distance from home is not a good indicator for how long I will be away (eg 5 miles walk to a local pub and a boozy afternoon by a log fire Vs 10 miles to a shop and back in 2 hours)
• How does the system decide how to arbitrate between 2 or more phone? (& not an easy algorithm as my wife often does not carry her phone with her, especially if I have mine).
• If the flow temperature is set low (good for boiler efficiency) then the warm up time, from cold, may be several hours. In other words geofencing would have to work with an 'optimum start' algorithm. If you were away for more than a few hours and you drove home at 70mph then the 'geofence' would need to be set at a few hundred miles away - is this really practical? If you fly home then it relies on the efficiency of your local airport - for me landing at our local airport to home is usually about 2 hours, ie the house would not be warm after a week away in Tenerife in the winter and the geofence was set at the airport.
• 'System Summary' screen is pretty useful in diagnosing issues, this should be more easily available  - I do not understand why this is buried on a hidden page on the hand held display and not available on the phone app.
• The schedule has a limit of 6-temperature changes each day - see part 1 on how we use the system - it would be better to have more.
• PC / Web version of the application software for easier schedule setting.
• Having a few labelled schedules (eg on the PC interface) would probably be useful (holidays, winter, summer, visitors staying, etc) - the system currently allows just one additional stored schedule.
• Data logging:
• good for diagnosing Evohome faults (log target and measured temperature)
• Helping to assess where the heating is working hardest (log target temperature, TRV demand and measured temperature). I think that this would help show where insulation would have the biggest impact and/or if a radiator is undersized.
• Synchronised demand. I have a theory that Evohome is turning the boiler off and on more times than is required and that this is wasting energy. This is just a theory and clearly depends on the boiler and my knowledge of boilers is almost zero...

...Just say that Evohome switches on radiator A  and the room with radiator B is at temperature and so the TRV is off. This will fire up the boiler. A little later room A gets to temperature and so the TRV on radiator A switches off. The boiler now turns off. A little later, the same happens with radiator B so the boiler is on again. Is there an opportunity to optimise this so that when the boiler fires up because radiator A is demanding more heat then the system checks for any other radiators that will need heat in the next, say, 30 to 60mins and turns on these TRV's (perhaps at a low %age demand) to give (some of) this heat early when the boiler is on anyway. I am not sure if this would save energy and I guess that it all depends on the current Evohome algorithm and boiler efficiency characteristics.

• I think that Evohome has the data to be able to provide a measure of insulation. I have seen figures quoted for insulation quality in terms of 'temperature loss in 5hours from 20degC inside when 0degC outside' (https://www.euronews.com/green/2022/12/09/europes-energy-crisis-in-data-which-countries-have-the-best-and-worst-insulated-homes). Since installing Evohome I have also put in some additional insulation - it would be really cool if Evohome could tell me if this has had an impact and how my home stacks up against others in the UK and elsewhere.

 

My view of Evohome after 3 Years

• Comfort: Evohome gives a much more consistent and controllable temperature through the house than our previous setup (ie thermostat in the hall, programmable timer and mechanical TRVs). The following are minor points in comparison to the previous set up.
• Our Kitchen temperature is not very even across the room; I think because the radiator and thermostat/TRV is behind a breakfast bar & there is limited air circulation with the rest of the room. The fact that we worry about this, & this was the case before we installed Evohome, tells you that we are getting to the finer points of getting good temperature control. I may experiment with a separate Evohome room thermostat, located elsewhere in the Kitchen.
• We have our flow temperature set at 65degC. I understand that a lower flow temperature would make our condensing boiler run more efficiently. However:
• As the boiler also heats our hot water tank we need a 65+degC flow temperature to avoid bacteria growing in the hot water tank.
• Our boiler model can achieve this with a weather compensation add on, but this means that the flow temperature will vary during the day. Question: will the Evohome self learning algorithms cope with an ever changing flow temperature? (see future blog post on weather compensation)
• Reliability:
• After the first couple of months I learnt how to fix the occasional (every few months), and undocumented, TRV fault and I now believe that, outside of battery failure, this is the only TRV fault that I have ever seen:
• TRV and physical valve being out of sync (eg radiator valve is off and the TRV 'thinks' that it has turned it on).
• I have not found any online guide as to how to fix this, but the following is quick and seems to work:
• Turn the TRV to +5degC and wait for the TRV to finish attempting to turn off the radiator (ie after any motor whirr has completed).
• Unlock and remove the Evohome TRV (slider the bottom of the TRV)
• With the TRV removed, manually turn the valve off (black knob/sprocket on top of the valve, that engages with the TRV) until you feel strong resistance, without forcing it)
• Replace the TRV and lock.
• Turn up the TRV to a high (radiator on) target temperature:
• The TRV will start to whirr and switch on demand (within a few seconds)
• Often, but no always, the TRV display then shows "CYCL" and, I think that, this indicates that the TRV is self-calibrating (ie finding the max on and max off end of travel for the valve). After cycling for a while (1 minute?) the TRV then goes to the set temperature.
• Hand held display battery life is a pain, especially when doing fault diagnosis. It would be good to be able to carry the handheld device from radiator to radiator to check demand against radiator temperature. The handheld display battery life does not allow for this, lasting only a few minutes.

 

Final Comments:

I would recommend Evohome if you want to control individual room temperatures and you are not a technophobe. With a few developments and better support materials, I think that Honeywell/Resideo could make this a more robust system suited to a much wider market.