Posted by: @hotheat

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Hi everyone, looking for a bit of friendly advice please

We have an 11.2kW ecodan, 300l hw cylinder and very basic Honeywell thermostat on a 4 bed detached house. Fairly newly installed but unfortunately installer is long gone without ever really going through the settings 

We’ve been using about 50kWh a day during the cold snap, which I think is probably about right however the house isn’t that warm. The pump seems to be using a lot then a little then a lot of energy, rather than the low steady use I think we should be aiming for (looking at the half hourly usage graph from octopus).

Our settings via thermostat have been to have it warm in the mornings, middling in the day (as not in), warm again in the evenings and then low enough to be off at night. This worked well enough before the cold snap but I don’t think it’s working now as it’s getting too cold overnight. the thermostat is in the hallway which is probably coldest bit of the house, so setting it to 17 actually keeps it on most of the time.

my question is: should I just whack it up to a higher temp 24/7 and have it on all the time? Reasoning being that once it finally gets there it’ll be able to keep it there? Or if not, how low should I go overnight?

the other complication is that I have no idea how the Mitsubishi control panel works. I know the compensation curve setting is on but I haven’t seen it activated I don’t think as it would say + some degrees in these temps? I think he said it’s set to 45 degree flow temp as standard. I also don’t know how to change hot water schedule - I think currently it’s on in the mornings which can cool down the house unhelpfully, although if I sort the heating this might not matter as much.

Is there a good YouTube guide on how the control panel works? And should I get a smarter thermostat, or is what I have fine?

any advice for a heat pump newbie gratefully received! Thank you

This one is a good explanation of different heating modes

and this one for timing heating/HW.

https://www.youtube.com/watch?v=FE9GfGLzsDo

The most efficient way to run it is on weather compensation.  Do you know if it is?  If not, try it and see what happens to the house temperature. If you set your thermostat a bit higher than you want you'll be able to see if the flow temperature is heating the house up to more than you really want. You can tune the weather compensation so that it gives the right temperature whatever the temperature outside.  That's what I do.  My house is a constant 21 deg even though my thermostat is turned up to 25. 

 If you want to set back the temperature when you're out then that's fine but only but 2-3 degrees.  

It's not worth getting a smarter thermostat because ultimately all it can do is switch the ASHP on and off.  If you want a better, more integrated wireless one get the one made by Mitsubishi.

Have a tinker and let us know how you get on. 

BTW 50 kWh is in the right ball park for this weather.  

@kev-m thanks Kev, that’s really helpful. So it is on compensation curve setting, but hw is on constantly - do you have any recommendations on if that’s best or if certain times is better? We have solar so in the spring/summer we’ll want it in the daytime for sure. There’s also a weekly immersion cycle for legionnaires that I’m not sure how to access when that is.

Should I turn it down 2-3degrees at night too? The issue is at the moment it’s really struggling to reach even 18 or 20 on the thermostat but heating eg the living room (which does get warm) all night seems wasteful! 

yes I’d be happy with c.50kWh a day atm and keeping us warm, but having had it on properly all day today it’s looking a fair bit higher than that already, so hoping there are some more tweaks I can make to improve efficiency 

HW depends on your usage pattern but if you can get away with once or twice a day that should be better.  Whenever HW comes on the heating stops so it's better if that isn't too often.  Also try and run HW either when it's warmest (normally mid afternoon) or when electricity is cheapest for you.

I'd definitely set back at night.  Ours is off via the timer 12-5, which does much the same thing. 

Having the thermostat in a cold hall isn't ideal - I assume it's not wireless?  If it can't be moved then you might be best to to set it a bit lower.

Legionnaires below.  Mine is every 2 weeks.

@kev-m that makes sense - it’s been doing the HW after we shower in the morning so the house isn’t warm yet and it’s made it worse, so I’ll tweak that.

The thermostat is wireless. Am I better off putting it in the living room and setting it to 21 then?

Thank you! 

Posted by: @hotheat

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@kev-m that makes sense - it’s been doing the HW after we shower in the morning so the house isn’t warm yet and it’s made it worse, so I’ll tweak that.

The thermostat is wireless. Am I better off putting it in the living room and setting it to 21 then?

Thank you! 

For the thermostat, yes, I would put in the living room if you can live with the hall being colder. A couple of degrees is normal but keep your door closed!

I have my HW on at 3pm only but we don't use much as we have electric showers and a dishwasher.

@kev-m thank you, one last question if I may! All my reading seems to suggest opening TRVs to full everywhere and leaving the system running at lower flow temp is the best way to run the system. I don’t know what my flow temp is, I just know it’s on weather compensation curve (and our hot water is piping hot atm) - so should I be opening all my trvs up? And if so, do I need to do anything to the ecodan settings to compensate? Installer left them at 4 in living spaces and 3 in bedrooms, which worked well before the cold snap. But yesterday we topped 70kwh and I think it’ll be more today with current settings

@hotheat, we've just published a guide by @heacol to piping, setting up and configuring a heat pump system to operate most efficiently that he has based on a recent study that he conducted (which we will look to publish shortly here on Renewable Heating Hub):

RENEWABLEHEATINGHUB.CO.UK "https://renewableheatinghub.co.uk/heat-pump-piping-and-operation-for-best-system-performance"

Efficient Heat Pump Tips | Renewable Heating Hub

Heat pump system design tips for efficiency—avoid costly mistakes and save on heating bills.

As part of his suggestions, he recommends removing all TRVs from rads (except bedrooms).

@editor thanks, I saw this and I won’t lie it panicked me a bit! I have Honeywell type valves, a third party thermostat, trvs, antifreeze and a buffer tank so it doesn’t seem good for me 😥

@hotheat, you are not alone. 99% of heat pump installations have been installed this way in the UK. Our system is the same – we have it all. Multiple Honeywell valves, buffers, etc. Don't panic though – it's the "standard" that the MCS and all installers seem to be sticking to and the point is you can still get your system more efficient despite some of the suggestions raised by Brendon.

Posted by: @hotheat

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@editor thanks, I saw this and I won’t lie it panicked me a bit! I have Honeywell type valves, a third party thermostat, trvs, antifreeze and a buffer tank so it doesn’t seem good for me 😥

Mars is correct, you don't need to panic, systems can often be improved without ripping everything out and starting again. It is often a matter of locating and rectifying the problems in a logical and systematic manner.

@editor Despite their other sins, documented elsewhere on this site, our MCS installer at least didn't curse us with third-party boiler-style thermostats, buffers or Honeywell valves... so it's not that MCS are requiring failure. This time, at least. I'm not sure I would have known to question the buffers or valves back then.