I forgot to add - when I was taking the flow/return temperature measurements, the outside temperature was reading at 6 degrees. 

@fleurcules

Welcome to the forum and hopefully we can help.  Im not a Grant expert but will try to offer general advice, but first a couple of questions/comments

1. Exactly which Grant model is it?  Im particularly interested if its R32 or R290? 

2. You need a copy of the installation and servicing manual for your machine, which will be on the Grant website, so you can tell what the fault codes mean. 

3. Is there a buffer tank/low loss header between the heat pump and emitters?  If there is a picture would help

4. When you are measuring flow/return , where are you taking the measurements.

Given what you say about the house its unlikely the heat pump is too small.  We need to get to the bottom of what the error is before going much further (hence question 1); If its the R32 machine then error A1 indicates a refrigerant gas fault which would need to be fixed first and would be consistent with it failing to reach temperature (and also likely very higg power consumption).

Once we have the error under control then we can look to the WC curve and operating mode.  You are right to think that the WC parameters dont make sense 52@5 means that it will never go above 52.  If it needs to be 52 @ 5 then at (say) 0 it will need to be higher.  Heat pumps are generally best operated 24x7 with thermostats and TRVs set to well above the desired temperature (so they have no effect) and the weather compensation curve adjusted (and if necessary rads balanced) to get the right house temperature.  

@jamespa thanks for your reply.

It's an R32, exact model is HPID17R32. My reading of the manual is that the error could either be because of a sensor issue, or a refrigerant issue. The person who came to do the service did comment that there was plenty of refrigerant in the system, if that helps (I don't believe he topped it up during the service). 

The measurements are what is shown on the control panel - I'm entering code 0100 to get the return temperature reading and 0109 to get the flow temperature. 

I think the answer to your third question is yes, but I'm not confident. I've attached some photos - the first is in the garage (attached to the heat pump) and the second is in the airing cupboard. 

The black cylinder in the second photo looks like an llh.  Is there a water pump nearby and how many pipes feed it?

You can't ignore the fault whether it's a sensor or an actual fault, either way it needs to be fixed.  That said if it has gone and is not recurring then maybe just maybe it's an artefact.  I had similar artefacts with my Vaillant all of which vanished once filters were cleared.

The salus, being a smart thermostat, is potentially causing a problem so I would turn the set  temperature on it up to say 30C to eliminate this possibility. Then check flow and return temp when you know the heat pump is actually running.  Also check what the heat pump thinks oat is.  If these don't correspond to the wc curve then it suggests the a1 error is real.  If they do correspond to the WC curve then it suggests that the salus needs to be permanently disabled (which is anyway the likely next step).

@jamespa the readings I have taken so far have been when the heat pump is running (and had been running constantly for multiple hours), so I don't think it's an issue with the thermostat. I'm already at the point where the heat pump is running all day even with the temp set at 18. 

When I've taken the readings the controller was showing outdoor temp at 6 degrees, so just one degree higher than the temp at which it should be targeting a flow temp of 52. At the moment I'm not even hitting the minimum target flow temp (which is set to 40 degrees). 

Posted by: @fleurcules

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@jamespa the readings I have taken so far have been when the heat pump is running (and had been running constantly for multiple hours), so I don't think it's an issue with the thermostat. I'm already at the point where the heat pump is running all day even with the temp set at 18

I hear what you say but I would still perform the experiment it to be absolutely certain.  Some thermostats, which should never be used with heat pumps, try to modulate the output by switching on and off periodically as the temp approaches the set temp.  

If you turn the thermostat up to 30 and the heat pump doesn't reach the required ft according to the WC curve then you know there is highly likely a problem with the heat pump which needs to be fixed before anything else can be done. 

Incidentally if you are successfully heating hot water (you don't say) then it's much less likely to be a problem with the heat pump in which case checking for certain by eliminating any effect of the thermostat is a must if you are to move forward. 

@jamespa we are not successfully heating hot water either. We thought we were, but have now realised that was only because the immersion was set to come on multiple times per week (which we have now adjusted down). Will try turning the thermostat up in any case.

Sorry missed your question re: water pump, have attached a photo.

Posted by: @fleurcules

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we are not successfully heating hot water either. We thought we were, but have now realised that was only because the immersion was set to come on multiple times per week (which we have now adjusted down). Will try turning the thermostat up in any case.

Ok please post back once experiment complete.  Give it a couple of hours to be sure.

Posted by: @fleurcules

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Sorry missed your question re: water pump, have attached a photo.

Ok looks like you have an llh which makes fault diagnosis more difficult unfortunately, but doesn't affect the need to do the thermostat test and conclusions it will hopefully lead to.

Record exactly what you do and observe, including any errors, so you can use it with Grant if a repair is needed.

If it doesnt reach temperature then the strong indications are its a heat pump fault, probably linked to the A1 fault code.  However you should first check that 'night mode' isn't enabled.  Assuming night mode isn't enabled then, to be absolutely certain, you could set the heat pump to run at a fixed flow temperature of say 50C (leaving the thermostat turned up), by setting 2100 to 0 and 2101 to 50 (or just leave it at the default of 45) and see what happens.  If it fails to reach temp with that setting and night mode isnt enabled, then I would say its more or less no doubt its a repair job.

If a repair is needed the it will need to be done by a proper Grant repair technician not an 'ordinary' installer.

@jamespa Ok here's an update on today so far. The heat pump has been on since 6am, I have turned up the thermostat. I've taken multiple readings of the outgoing flow temperature and all have been 34 degrees (OAT at either 5 degrees or just under), apart from during a defrost cycle when it dropped to 29, then quickly got back up to 34 once the defrost cycle was done. I have made sure night mode and low tariff mode are disabled.

As a final step I've now just set it to fixed flow temp mode - temperature was set at 52 but I've lowered to 45. No increase from 34 yet but I'll check back in a bit. 

Posted by: @fleurcules

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@jamespa Ok here's an update on today so far. The heat pump has been on since 6am, I have turned up the thermostat. I've taken multiple readings of the outgoing flow temperature and all have been 34 degrees (OAT at either 5 degrees or just under), apart from during a defrost cycle when it dropped to 29, then quickly got back up to 34 once the defrost cycle was done. I have made sure night mode and low tariff mode are disabled.

 

As a final step I've now just set it to fixed flow temp mode - temperature was set at 52 but I've lowered to 45. No increase from 34 yet but I'll check back in a bit. 

 

Thats getting pretty convincing.  Remember also to check that Night Mode isn't in operation.

@jamespa yep mentioned in my previous message I've disabled night mode.

It was sitting at 35 for a bit, now up to 36. Although oddly the rads have just gone from feeling about as warm as they ever do to feeling noticeably colder.