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Thread: Evohome, advanced load scaling and cold weather boost

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  1. #1
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    Default Evohome, advanced load scaling and cold weather boost

    I wonder if any of you could help me with this.

    We have had Evohome for quite a few years now. It's worked flawlessly, keeping to setpoints and utilising optimum start really well. However, since the inclusion of advanced load scaling and cold weather boost things have started to go awry.

    Over the last few weeks as well all know the weather conditions have fluctuated quite a lot. This has led to days where the system has applied cold weather boost along with optimisation to get rooms to temperature at set point. The problem is they never do.

    For example today our downstairs room sat steadfastly at 3 degrees below setpoint. The system parameters screen showed the BDR91 at no more than 40 percent with the downstairs area showing as 100. The flow temperature for the boiler is set at a maximum of 70 degrees for CH. This leads to the actual flow temperature being too low to heat the room. The room is set to be at 19 degrees (boosted to 20) by 5.50am. My wife eventually gave up waiting for it to heat at 11am and set the temperature to 21 degrees. This activated the boiler and the room heated.

    Our load scaling is set to normal. I have tried partial in the past few weeks to see if that helps but to no avail.

    We are using the evohome unit as the temperature sensor in the downstairs zone, but this problem is replicated across the house - when the temperature is cold the system seems slow to react to the changes and the setpoint is never reached on time.

    I am thinking of swapping out the BDR91 for an Opentherm bridge. Our boiler is an Atag installed last year and I considered at the time to change it then but was talked out of it by my installer as he said it wouldn't be worth doing. Should I just bite the bullet and do the swap? Will this work better?

    It has become really annoying as like most people on this forum I just want the system to work without much interaction. For us at least this software update has been a step backwards.

  2. #2
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    If your system has been working well for several years, why not turn off the “advanced” features and continue as before? There is no guarantee that a new boiler will make things work as well as previously. I would be inclined to follow the advise “If it is not broke, don’t fix it”.

  3. #3
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    Can see your thinking but the whole idea of a new boiler plus the new features was to reduce the gas usage. I have today switched off the new features. At the moment my daughters room is half a degree below setpoint. The boiler demand is showing as 100 percent, which will probably lead to an overshoot, plus the boiler return is above 55 degrees which means its not condensing. If I switch on load scaling as before the boiler demand instantly reduces to 43 percent. This will now reduce the return so more condensing means less gas use.

    The question remains, why doesn't the load scaling work properly? This morning the temperature downstairs was 2.5 degrees below setpoint, 100 percent demand from the zone but only 16 percent from the relay. Whichever way you look at it there is something wrong there.

    I'm going to persist with load scaling for the time being, but with cold weather boost off, see what happens, but if there is still anyone from the Resideo team on this forum I wold be grateful for a PM.

  4. #4
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    Great if you can get the load scaling working properly, but you would need to save a lot of gas to pay for a new boiler unless you needed one anyway. What temperature is the boiler set at, would tweaking it down a bit help? I was not on the beta trial so hopefully some of those with experience of the new features will be able to offer some more informed advice.

  5. #5
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    I’d always recommend using OpenTherm if you can, sounds like your installer is not familiar with its benefits.

  6. #6
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    Quote Originally Posted by kevinsmart View Post
    Iíd always recommend using OpenTherm if you can, sounds like your installer is not familiar with its benefits.
    I have found many installers, indeed if not most, are completely unfamiliar with the actual setup and running of a system. Installing the boiler fine, but today with system controls we have there are the niceties of it running at its plus 90% efficiency that are not known about. Things like for example, not checking if the mains water pressure is to high or indeed too low, checking the size of boiler needed, checking of the size of the expansion vessel when the system is used at various temperatures is adequate for the house, knowing where to wire controls such as Evohome, how OpenTherm works. I know of one Independant site whose researches ascertained that over 90% of installers do not set an installed system up correctly to enable it to be 90% + efficient. For central heating purposes boilers donít have to have a massive kW rating.

    Yesterday I was told the story of a chapís neighbour whose installer advised he needed a combi boiler to replace his existing one. The house is a 5 bedroom, stone built property with 3 bathrooms. Even I know he will struggle. No mention of a system tank for the size of property. The house still did not seem to get warm so the same installer advised they needed to replace the radiators. From what was described to me the installer had no knowledge of system needs, balancing and usage. The cost to the person of all this so far is £9,000.

    Thus I believe that manufacturers need to do a lot more with the installers to ensure they properly understand what they are installing and how to set it up. You would not install a car engine and walk away without ensuring it runs properly!

  7. #7
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    Thanks for the replies

    We needed a new boiler as our old one was on its last legs. As I said before at the time I asked about Opentherm and also Weather Compensation and the installer said as we already had Evohome and that because the new firmware was on its way, changing to either of those wouldn't make a difference.

    But the new firmware just doesn't seem to be working. Again this morning it has allowed the temperature to drop 2 degrees below the setpoint, with 100 percent demand for the zone, and 8 percent for the BDR91. The only way you can stir it into action is to do a manual override. Soon as you do that, 100 percent demand at the boiler.

    Thinking now I'll go with my gut and have the Opentherm bridge installed.

  8. #8
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    Apologies, I have reread your original post and now realise that you have already got a new boiler, I thought you were considering changing boiler for a opentherm compatible hence my comment, my mistake.

    I think I would be inclined to opt for an opentherm bridge, but I am not convinced that it will solve all your problems but, as I said, I do not have the new EvoHome firmware, so am not in a good position to advise and will shut up now.

  9. #9
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    Quote Originally Posted by sminkypinky155 View Post
    I wonder if any of you could help me with this.

    We have had Evohome for quite a few years now. It's worked flawlessly, keeping to setpoints and utilising optimum start really well. However, since the inclusion of advanced load scaling and cold weather boost things have started to go awry.

    Over the last few weeks as well all know the weather conditions have fluctuated quite a lot. This has led to days where the system has applied cold weather boost along with optimisation to get rooms to temperature at set point. The problem is they never do.

    For example today our downstairs room sat steadfastly at 3 degrees below setpoint. The system parameters screen showed the BDR91 at no more than 40 percent with the downstairs area showing as 100. The flow temperature for the boiler is set at a maximum of 70 degrees for CH. This leads to the actual flow temperature being too low to heat the room. The room is set to be at 19 degrees (boosted to 20) by 5.50am. My wife eventually gave up waiting for it to heat at 11am and set the temperature to 21 degrees. This activated the boiler and the room heated.
    If your boiler is leaving rooms at 3 degrees below their set points with a 40% TPI duty cycle then I'm pretty sure that your boiler is struggling to put out enough heat for the number of radiators you have or your radiators are undersized. What average flow temperature is it producing in these conditions and what flow temperature does it peak to in each 10 minute TPI cycle? How hot are the radiators in the offending rooms?

    A 40% TPI demand will take longer to reach the set points than 100% (that's the idea, as load scaling helps avoid room overshoots) but the set points should still be easily reached if your boiler has enough oomph to reach the maximum set flow temperature in each 10 minute cycle.

    Sounds like it doesn't, and the problem was being obscured by Evohome regularly calling for 100% heat from the boiler.
    Our load scaling is set to normal. I have tried partial in the past few weeks to see if that helps but to no avail.
    Quote Originally Posted by sminkypinky155 View Post
    Thanks for the replies

    We needed a new boiler as our old one was on its last legs. As I said before at the time I asked about Opentherm and also Weather Compensation and the installer said as we already had Evohome and that because the new firmware was on its way, changing to either of those wouldn't make a difference.

    But the new firmware just doesn't seem to be working. Again this morning it has allowed the temperature to drop 2 degrees below the setpoint, with 100 percent demand for the zone, and 8 percent for the BDR91. The only way you can stir it into action is to do a manual override. Soon as you do that, 100 percent demand at the boiler.
    If you are seeing crazily low heat demands for the boiler with high demands from zones like 8% boiler from 100% zone, change load scaling to partial mode. I know you said that it doesn't make a difference but trust me it does... my system is unusable in normal load scaling mode but works well in partial mode. When you change modes it will take a couple of days to adapt fully.

    I've discussed this problem (excessive scaling down of the load in Normal mode) with the Resideo guys in the beta firmware thread and I'm not convinced that they believe this is a real problem but from my perspective it's a known problem, and certainly one I experience on my system.

    However apart from using Normal mode when you should probably be on Partial I think your underlying problem is your boiler just can't cope with the load the radiators are presenting to it at anything less than 100% TPI duty cycle. In this case load scaling is never going to work properly, so you need to look into this to find why the boiler is struggling so much.

    More info about your boiler - model, total output in kW (some boilers can be turned down to lower power levels) how many radiators you have of what size, insulation in the house etc might help people to judge whether there is an issue here. It could be something as simple as someone has turned the maximum kW output setting on the boiler down too low - this is independent of the flow temperature setting and is usually hidden in the installer menus.
    Last edited by DBMandrake; 4th March 2021 at 12:12 PM.

  10. #10
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    You say your new boiler was installed a year ago. Was everything working okay with the new boiler for a reasonable period prior to the EvoHome firmware update?

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