Heating not coming on with air source heat pump

Eckie

Hi all, looking for some advice.  We have just had a Grant Heat Pump installed.  The only issue we have is the heating is not coming on as scheduled.  The water cycle takes precedence, of course, but even when there is not hot water demand the heating will not kick in.  The only way we can get the heating on is to either turn the water off or reduce the water temperature set point to 45 degs C, from 55.  
Has anyone else experienced this and what might be the solution?
Thanks

lohr500

Can you not ask the installer to return and sort it out?

matelodave

There really isn't much point in asking us to guess how yours has been installed or set up unless you can tell us exactly what you've got, how its been installed and how the controls and parameters have been wired and configured. There are far too many variables.

Have you checked the installation and user manual to compare how it should be configured against the installation and control settings on your equipment.

If it's not working as it should or you don't understand how to operate it then get the installer to sort it out.

DougMLancs

What’s the desired house temperature? It won’t come on within it’s scheduled period if it’s already warm enough. Mine was fitted 4 weeks ago and it’s never had to do a heating cycle yet. As a side note, the installer should ideally have set the heating to run on weather compensation so it looks after itself rather than on a schedule. You’ll appreciate the efficiency increase come winter!

MultiFuelBurner

Eckie said:

Hi all, looking for some advice.  We have just had a Grant Heat Pump installed.  The only issue we have is the heating is not coming on as scheduled.  The water cycle takes precedence, of course, but even when there is not hot water demand the heating will not kick in.  The only way we can get the heating on is to either turn the water off or reduce the water temperature set point to 45 degs C, from 55.  
Has anyone else experienced this and what might be the solution?
Thanks

It sounds like maybe the hot water is set to on 24/7 combined with the fact it is warm and your thermostat hasn't kicked in for the heating.

All pure guesses of course and you really need to provide a lot more info.

Reed_Richards

Eckie said:

The only way we can get the heating on is to either turn the water off or reduce the water temperature set point to 45 degs C, from 55.  

This is a pure guess, I have a heat pump but not one made by Grant.  My heat pump cannot, quite, heat the DHW cylinder to 55 C.  It can get it up to 50 C, perhaps a degree or two more but to reach a higher temperature it has to turn on the immersion heater.  Now if for some reason the immersion heater was not working it might get stuck forever trying to get the hot water to a temperature it cannot manage.  Since the hot water takes priority over the central heating, this could give the symptoms you describe.   

Cardew

DougMLancs said:

 As a side note, the installer should ideally have set the heating to run on weather compensation so it looks after itself rather than on a schedule. You’ll appreciate the efficiency increase come winter!

I don't think all heat pumps have weather compensation.

DougMLancs

Very nearly all do (although less knowledgeable installers might bypass it) and it’s mandatory for an MCS installation in the UK. Not all call it that mind you, some call it something like AI or auto-adaptation. Some ground source models don’t however or the Dream stuff you see on eBay. A modulating heat pump without some form of weather compensation isn’t worth having.

MikeFl

I have a Grant (I think with Installation Pack C) and the set-up can specify DHW Priority (as you seem to have) and maximum time for DHW and minimum time for CH (during a DHW heating cycle); mine are set as following:

(31 21) Maximum DHW time = 60 minutes

(31 22) Minimum CH time = 0 minutes

I think this means once a DHW cycle starts it will be 'on' for 60 minutes (even though it might reach the desired temperature in less than that); and CH will not run at all during that time. This might be what's happening with you.
(NB. these settings of 60 and 0 are recommended by Grant in their installation guide)

My installer had set the DHW cycle for 3 x 1 hour periods throughout the day, which is way too much for my needs, so I reduced that to once, in the afternoon when outside temp is highest for most efficient DHW heating. 

I would suggest checking the "31 nn" parameter values on the un-friendly controller.