@sandman1600 

Hi. Without knowing more about your system for a quick and dirty fix I would lower your flow temperature to 35C and leave the heating on all the time with a setback overnight if you want. If the rooms don’t get hot enough then dial up the temperature day by day until they do. Be aware your concrete floor make take days to fully heat. 

As a longer term solution you need to investigate the weather compensation settings on your unit. Others on here may be able to help. 

There are 2 important fixes in first instance. Then you can try further small tweaks.

1. Get off Fixed temps and onto weather compensation. I'm sure you can get help in this forum for your specific make & model. Also try Facebook user group for that make. Typical savings 20% or more. Some cases over 30%

2. Check Time of Use tariffs to see if any make sense for your setup. Depends on exactly what you have e.g. batteries, e/v or none etc. Most ashp users can do better than standard/fixed tariffs. In my case its right down at 8p kwh. But helped by batteries & e/v

Posted by: @sandman1600

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Is it better to set it to a 55 degree flow temperature and let it heat up rooms a little quicker and not be heating as continually. Or is it better to be running more at a lower temperature?

As others have implied, the latter (this is the most important thing to understand about heat pumps). 

In short the procedure is:  

• Set all your thermostats to maximum so they are always calling for heat, turn up and TRVs/thermostatic zome valves to maximum, set your heat pump to run and heat 24x7.  
• Turn off any 'autoadapt' mode on the mitsubishi if its on (probably not if you are running of fixed flow temperature)
• Set the 'high OAT' end of the WC curve to 25C(FT) and 16C(OAT)
• Over a period of time drop the 'low OAT' end (the FT at your design outdoor temperature or thereabouts) of the WC curve down as low as it will get while just heating the house to the desired temperature.  Once it gets close make changes slowly, no more than 1C per day, reducing to 1C every 2 days as it gets closer.

I would expect the low OAT FT to be something like 35C as suggested by @bontwoody, so Id start there.  55 is a crazy flow temperature for UFH, this was obviously set up by someone who knew nothing about ASHPs!

You may find, particularly in milder weather, that it cycles like mad in which case there may be a case for part time heating.  But until you have got the basics right based on 24x7 operation its not worth going there.  

As @tim441 says ToU tarifs can also make a big difference, but I would strongly recommend first to get the basics right.  The cost should work out roughly the same or a bit less than oil (over a year) once its properly adjusted, quite a bit less if you can take advantage of a ToU tarrif.

Hope that helps - please report back how you get on.  Can I suggest you also read this guide to the basics of ASHPs, it will help make sense of things

@sandman1600 

I have a Mitsubishi Zubadan 14kW in a 220m2 barn with mostly Jaga fan-assisted rads.  At the moment the Weather Compensation (WC) curve is giving a LFT (Leaving Flow Temp) of 37C with the OAT at 7C.

I haven't changed the pre-set WC standard curve, but usually run the LFT at -4C    i.e. 4C below that curve.  You can easily adjust this + or - on the main screen of the controller.

You will discover that ASHPs like an easy life - they can use a lot of power when asked to either (1) regularly start up from cold or (2) generate a high flow temp from a low outside air temp (OAT).

So if you can avoid those things they will return the favour with low energy demands.

Hence the advice to keep the unit running "low and slow", consistent of course with keeping the house warm.

@bontwoody thanks very much for that. 

Weather compensation is something we really need too look at. The installers told us not to bother with it. 🤦🏻‍♂️

@tim441 Thanks for that. The Weather Compensation settings are definitely something I need to get my head round. The installers told us to ignore that setting. Definitely makes sense though. 

I’ll look at tariffs too. We are hoping to get solar panels installed sooner rather than later so hopefully that will help to lower the bills a little too. 

Posted by: @jamespa

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In short the procedure is:  

• Set all your thermostats to maximum so they are always calling for heat, turn up and TRVs/thermostatic zome valves to maximum, set your heat pump to run and heat 24x7.  

Thanks for the extensive info here. Can I just make sure I understand this…  so the idea is to ramp up the thermostats so that there’s a constant call for heat from the ASHP and to avoid the temperature drops?

And then we lower the flow temperature and just adjust to balance out until we’re getting the desired constant temperature at the lowest possible flow temp?

is that correct?

I appreciate that we then need to sort out the weather compensation too but I just wanted to make sure that we had the right idea before we start messing  

Apologies if I sound thick with any of these questions. I’d never heard of most of this terminology and acronyms until this week. 

Posted by: @sandman1600

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The Weather Compensation settings are definitely something I need to get my head round. The installers told us to ignore that setting.

That's really scary, of all the settings it's the probably most important one, and one which the installers cannot possibly get right because they don't have the time that's needed.

Posted by: @downfield

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@sandman1600 

I have a Mitsubishi Zubadan 14kW in a 220m2 barn with mostly Jaga fan-assisted rads.  At the moment the Weather Compensation (WC) curve is giving a LFT (Leaving Flow Temp) of 37C with the OAT at 7C.

I haven't changed the pre-set WC standard curve, but usually run the LFT at -4C    i.e. 4C below that curve.  You can easily adjust this + or - on the main screen of the controller.

You will discover that ASHPs like an easy life - they can use a lot of power when asked to either (1) regularly start up from cold or (2) generate a high flow temp from a low outside air temp (OAT).

So if you can avoid those things they will return the favour with low energy demands.

Hence the advice to keep the unit running "low and slow", consistent of course with keeping the house warm.

We’re in a 130 m2 split level bungalow so that’s really encouraging. We’re not exactly hermetically sealed but we’re pretty airtight and insulated so fingers crossed we can make it work for us. 

I’ll maybe just turn on the pre-set curve option initially and then start to tinker as I get a better understanding for how it’s all working.

Thanks very much for the info  

Posted by: @jamespa

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That's really scary, of all the settings it's the probably most important one, and one which the installers cannot possibly get right because they don't have the time that's needed.

I get the impression that they’re just trying to replicate a conventional boiler for people. Which is utterly nuts but I’m guessing it makes life easier for them. 🤦🏻‍♂️

@sandman1600 Yes, you have the idea of what you need to achieve. Ive no doubt you will see much reduced energy usage very soon. 🙂