Hot water and heating control with my Mitsubishi Ecodan Air-Source Heat Pump (ASHP)?

@Caroline2000 just to confirm, the electrician confirmed that the fuse (where is the fuse in a heat pump?) had gone. So it needs replacing does it? He also confirmed no power to the pump? How is the underfloor heating working if the pump has no electricity?

A heat pump needs an electric source. There are 2 13A spurs…..one has just melted! The U/F heating and DHW are on 2 different loops, hence one is affected and the other not

We don’t have Melcloud. We have now got hot water but it’s using the immersion only to heat which isn’t ideal

Did you find the solution to this problem? If so tell us

Our electrician friend has bypassed the fuse/spur - still amped via fuse box in garage so safe. Allowing immersion to come on. He thought the pump must be broken but he’s said it’s a very simple Groundfos CIL2 pump so shouldn’t be an issue. He thinks that the pump wasn’t kicking in as the temp was below the settings we had set for when it would heat water (he thinks maybe to protect airsource during very cold weather)

The water temp is now above this minimum level (thanks to the immersion working) and it seems to have kicked the air source unit/pump attached to tank into action.

We are keeping our fingers crossed as an issue with the FTC would be very expensive to fix!

It sounds like the fuse that's blown was for the immersion heater, not the heat pump. I would get a proper electrician to fix it because bypassing it is potentially dangerous.

Heat pumps don't have a minimum water temperature below which they won't switch on. That would make no sense as it would stop the heat pump reheating the cylinder if you used all the hot water. I'm pleased it's now working but I wonder if there was a problem with your settings.

Obviously it needs fixing - we need a new spur switch/fuse which is getting done today.

The friend is a qualified electrician, qualified to work on high voltage installations off shore as well - so trust he knows what he’s doing!

We have had this system since 2019 and got the most part works fine. Biggest gripe is the cost to run it…..£6000 a year at the moment - hopefully a drop in electricity prices will help 

Our settings were to heat water once it dropped around 20 degrees from target temperature 

Yikes, unless you have a huge house heated to tropical temps that’s far more than it should be. Sounds like there’s something not set up right. Are you still in touch with the installer ? Do you know what COP you’re getting?

If you describe your system components and settings here there are a number of heat pump owners keen to help improve the performance for you. It may be just a few settings that can be altered.

It’s the heating that is the biggest cost, specifically the wet underfloor heating downstairs.

When electricity was 13p/unit the summer months were around £60/month.

The original installer came out a few times, but said it was fine…then seemed to go AWOL/MIA…..got some advice from a forum to fiddle around with the compensation curve - that helped a bit; but the increase in electricity price pretty much tripled/quadrupled the cost.

Where do I find the COP…I do recall having this at the start…now we just try not to think about altering settings as it was driving us crackers!

House is quite big, but it’s never tropical…..just about warm enough in winter to get by!

Once I get the fuse/pump sorted I’ll post our settings and see if it can be improved.

Just to add…when I refer to the pump, Im taking about the small pump device attached to the mixing tank…not the ASHP outside.