So here we are, brand new Grant ASHP installed…

It's ran over night, panels calibrated.  Am not seeing much promise from it, and I'm not surprised.

I'd brutally honest have thought the installer would go around and bleed rads to be sure no air (which would hamper seeing 21C) - he didn't.

I've been told to give it 24 hours from last night.  But I have a simple understanding of how heating to 21C would work - you'd expect an upward trend.

This has seemed to have currently plateaued…

So the installer set (after I was talking about noise from pump room speed, I didn't insist on changes):

• Grant ASHP at speed 1/3
• Pump room speed at 1/3
• Flow setter adjusted to get flow to around 28L/min
• Altered the WC (didn't seem to go with Grant default 45=40, changed to -3 at bottom from -4, 19 max ambient, 25 min flow, 40 max flow) - that in fairness isn't a wild W/C

Also told him multiple times that the Grant engineer for whatever reason set the UFH pump to speed 3 (seems crazy to leave it at that).

Last night I think, mmmm temps aren't really going up as expected (I'd seen on the supposedly 'broken' ASHP that it would recover faster from cold than this).

Check the flow rate, 12L/min.  I have seen up to 20L/min, but was on a defrost cycle, and the second time I saw it could have just been right after one (it's -1C outside for context).

So now we have a system running with a low water flow rate.  And underfloor pump before manifold at max speed.

I presume the temps not really going up is likely due to those factors, as saw higher temps with smaller LLH and 'broken' ASHP.

The ASHP and pump room pump, were always 2/3 both sides previously.  I'd have thought adding in 50L LLH would want them up, not down, but I have no idea tbh.

Currently seeing:

• Kitchen (UFH): 19C (Heatmiser panel)
• Yes the panel is calibrated to be -1C to match my new Testo 915i probe (I equipped myself with something accurate to ensure I was being fair to installer).  - this matches the room well.
• However, previously it would get to 21C (so say 20C - but the panel would stop it at 21C, it probably could have gotten up there)
• Hall: 18.7C (Heatmiser panel) (reminder this drives the ground front zone - 2 living rooms, 1 hall, 1 WC)
• Living Room 1 - 17.4C (temp wired Heatmiser panel)
• Living Room 2 - 17.8C (temp wired Heatmiser panel)
• Landing (upstairs) - 19.8C (Heatmiser panel)
• Utility (UFH): 21C (Heatmiser panel) - this room is tiny, and has the plant room cupboard, if it wasn't 21C, I'd be seriously worried

In about 2 hours I've seen zero upward trend.  From last night a fluctuation of maybe 0.3C from then to now (but that was at night, there's low winter sun = solar gain etc etc).

There's currently no set back either, so it's not a recover from setback situation.

Really not sure what to think anymore.  I am between a rock and a hard place.  November 26th = rumoured that the £7.5k BUS could be scrapped.

Unbelievably I'm 2 years into all this and haven't got that for obvious reasons and it's likely at serious threat.

I'm not touching anything in the system as the installer is monitoring temps.  I presume he's rather worried as asked me to move the 2 temp wired panels from near the log burner slate hearths to hang them over the doors.  Yes slight uplift, but not enough to turn sub 18C to 21C…

Posted by: @crimson

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Check the flow rate, 12L/min

So at DT 5 (the normal design DT for heat pumps) that will transport 4.2kW (assuming water, about 10% less if its glycol).

Is that sufficient, if not then DT will rise (which has the effect of reducing average emitter temperature and thus output from the emitters - just like reducing flow temperature) until the system is in equilibrium at a lower than designed room temperature.  The physics is really, really simple, you learn it at the age of about 13!

Nothing more to say.

Yeah, no idea why he thinks 12L/min is ok.  He even showed me it running to 28L-30L/min yesterday.

Going round the houses on this stuff.

Irony is - brand new ASHP heatpump + 50L LLH for the water volume issue (in a LLH, not a volumiser!!) = worse performance than before (which wasn't good enough mind, but not this bad).

Just baffles me they won't try getting the LLH off the flow.

I can see with the Amazon probes (recommended on this forum in January 2024 - that aren't far off the Testo 915i!!) - that the temp on the flow pipe from the ASHP, to the temp going to just before the heating zones (after LLH and pump room pump) - shows a drop.

The low flow is causing distortion/mixing etc in the LLH = not enough water temp to emitters.  Simple as that.

In fairness, when installer was here yesterday - those 2 temps were pretty spot on.  However adjusting pump speeds and flow setter then leaving within 5 mins - to me seems a really bad move.

Fixing the flow rate (sorting pump speeds) - I don't believe will actually fix my issue, as the temp drop seen from ASHP, past LLH and pump rooms pump to before zones was only 0.5-1.5C anyway.  All I have is just a bigger LLH in the way.

The issue has been it seems to me, the delta with the LLH kept narrowing = cycling off of ASHP.  Avoid that by NOT HAVING A LLH!!!  NOT A BIGGER ONE!!!

So I've given him the clue the flow setter reports 12l/min, he's said it's fine.  They've got till tomorrow morning, and I can see forecast is -2C, so I'm pretty certain, it won't go up…

I truly hope the builder takes this as the installer just simply cannot get this running and he deploys the specialist.

Least if we get the LLH off the flow, we have a digital flow setter that never allows misreading, we have a smart panel that doesn't require me to report in issues (that installers ignore).

The datas there + the actual flow from the ASHP gets to the rads.

If that fails, then the rads/calcs need looking at, yet again.  I even have written record of me saying go even wider with the Eskimos, now's the time, but was assured - the rad uplift would work (that was September 2024, it helped, but didn't 'work').

I've even checked for Stelrads (only rads these guys seem to know to use) - none that fit have the output.  Grant engineer suggested their alluminium rads - none of those that fit have the output.

This is all never mind the fact that early on in this thread people pointed at the pipework being undersized (22mm/15mm plastic = smaller bore down to 15mm copper to rad = hampers flow).

So that's likely not accounted for, having 3 pumps (ASHP, pump room pump AND a pump before UFH) = lots of flow issues, plus narrow pipes to contend with.

All routes, (and it's been said by members on this thread from the get go), come to the conclusion that a LLH in this situation is just never going to work/hamper it.

I've just had an installer that won't accept that and points at every other element in the system as the fault…

Save yourself some angst.  Until the flow rate is fixed there is nothing worth speculating about. 

Once its fixed then measure the temp drop across the LLH and what happens to the rooms, and then some further deductions can be made.