If you can get them to focus on the flow rate, which seems to be the main issue. Playing around with the HP parameters is really tweaking to help with efficiency, and fiddling there can muddy the waters. If the HP isn't delivering sufficient heat to the building, then you'll never get anywhere.

It could be related to the LLH although it seems to have an automatic air vent so it ought to be full of water (they don't always work though), and your pressure seems fine.

Good luck. Hope you get somewhere with them.

Looks like I have same brand LLH as this one:

https://renewableheatinghub.co.uk/forums/postid/13456

Posted by: @allyfish

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Posted by: @crimson

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'll periodically check that and raise with plumber.

Hi @crimson, the flow rate is constant for Grant systems, as they have a fixed speed pump in the ASHP. If your primary flow rate is 9l/min, and the flow valve isn't sticking [give it a gentle tap, but you can usually see it moving slightly] then something is very wrong with the primary flow. There will be nothing wrong with the Grant Aerona unit, they are very reliable and dependable, nearly all issues arise from poor installation and deficiencies or shortcomings there.

It looks to me like the primary flow rate on your system could be seriously deficient. If it is much lower than the secondary flow rate, what happens is return water from your radiators going back to the ASHP mixes with the heated flow from the ASHP in the low loss header, lowering the supply temperature to the radiators and emitters. Then you've got a shortfall in heating capacity. It's easy to check these things, and a competent plumber should not need to be prompted to do so. Ideally, systems are best without low loss headers, but Grant specify them as do other ASHP manufacturers to give a little wriggle room in system design and make flow rates less critical.

A bit of info for you, and maybe your plumber too if they are not up to speed: https://www.heatgeek.com/low-loss-headers/

Lower primary flow compared to secondary flow produces the effect circled, it needs to be fixed and balanced up. Grant ASHPs have pretty good primary flow pumps, and the piping route is usually very short between the unit and the low loss header, so this problem is rare. There will be a cause; such as a closed valve (maybe the flow setting valve), or that strange black 4-port mystery valve (the function of I have no idea) or the pump speed setting on the ASHP control PCB. They are normally supplied set to max speed, and usually need turning down not up.

 

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On this obviously not accurate but top right much hotter than top left to touch. At one point top right was very cold to touch v top left. Currently bottom feel almost same, a lot cooler than the top pipes. Again this is by touch so zero accuracy

Oh and the lower 4 port mystery black valve. That’s connected to a water softener

Plumber's been.

Changed fuse for hot water panel, nothing going to it, so that's now on the electrician to come.

I asked about the valves closed - turns out all are open (just the orientation of them confusing in a photo).

The LLH, I questioned why not the Grant one, his explanation was that has a built in immersion which they don't need.  Grant pointed them in the direction of the standalone one in there.  He also mentioned due to the size of it it wasn't practical.

I then asked is this a heat calc issue, unbeknownst to myself the architect heavily queried the plumber's heat calcs so asked them to get a second opinion which Grant inputted into, and made size recommendations for their kit off the back of it.

Plumber is now contacting Grant, he said that flow rate is coming from the ASHP itself? and far far too low.  He tried to alter it that valve with that screw, it bounced but never went higher than what's seen in the photos, was fully open anyway.

As the system was turned off so he could change the fuse, he then checked how quickly it came up to temperature and seemed to have no issues, pipe coming in very hot.  But flow rate doesn't change.

He's now requesting Grant come out to investigate.

@crimson small steps towards a resolution. The flow rate is a biggie, that needs fixing. That will be throwing a spanner in the works in the LLH if the secondary side flow is much higher, which it should be. Grant really should specify the fitting flow indicating valves on both primary and secondary sides, not just primary side, as that would make checking flow rates so much simpler when commissioning and ensuring pump speeds set to are optimal for best efficiency and lowest running cost.

There's very little or should be very little by way of fittings and pipework on the primary circuit between the ASHP and the LLH, so the very low flow is unusual. Could be the pump speed setting, which I hope the plumber has checked, but assuming that's on speed III, then that leaves very little else - piping & flexible hoses, maybe frost protection valves. All should be 28mm. There's no filter or strainer inside the ASHP, so nothing to block up there, but a check of the condition of the Grant magnetic filter unit would give a clue as to whether contamination or a blockage is causing low flow. For a new install everything should have been power flushed through before commissioning. Grant probably need to look at it, but I would wager they find an issue on the system side and not with the ASHP. Hope you get it fixed up soon!

So no call from Grant yesterday. So I rang up this AM and was told if engineer visits Monday and it’s not manufacturer fault it’s £150 plus £60 an hour charge to myself.

I got onto builder and plumber and architect this morning and quickly got a message from Plumber that he’s visiting today to sort it.

After a good long while of him being here. He fully replaced the panel for the hot water after checking the wiring and finding fuse had gone again. Looks like panel itself faulty. Soon as replaced it came on. He then tested the ashp doing the hot water with a manual boost. Found the top left pipe from LLH going to hot water/heating wasn’t matching the top right (which was hot). After a lot of investigation of wiring etc in plant room and ASHP to ensure nothing electrical. The  check valves. He dropped the speed the second pump runs at from its fasted (setting 3) to slowest. Then the temperature of the pipe starting coming up and we saw the water temp on the tank coming up. At end of 2 hours (he’d left by that point understandably), it got from 19c to 47c. So now I have ASHP provided hot water.

I’m now seeing by having the auto hot water run off for rest of the day how the heating itself gets on.

Some progress on the hot water. Reducing the flow on the secondary side to balance with the deficient flow on the primary side is a sticking plaster. The primary flow needs to be 30litres/min or thereabouts as does the secondary side. That’s a must fix for the plumber. If it’s it fixed you’ll get nothing like 13kW of duty out of the unit. 

Yeah not quite sure what’s going on with the flow. Interestingly now I’ve been given more of a tour the flow rate is on the bottom right from the bottom right pipe out of LLH. Just after the Mag One filter.

Top left pipe just not warming up. Which explains why heating is dire and rads not warm

No chance of heating. Top left pipe not getting heat whatsoever. Which explains why rads never warm. It’s been nearly 3 hours so I’d expect some rise but nothing. Its not like the ASHP isn’t providing heat

Plumber is going to contact Grant it seems.

Just very odd only top left pipe to LLH is hot. All other pipes cool to touch. Can’t workout where the heat is going. Hot water hasn’t run again, will run 3-4am. That temp has slowly gone done from 47c at 3 pm to 43c at 9:30pm so it’s not like that’s run again without being programmed too (not that it would).

complete layman here but in any scenario could literally the water flow just simply be almost stuck going into LLH and nothing passing through? It literally feels like no heat is going from right to left (outside to inside as it were).

Apologies for string of posts but putting down findings soon as I have them.

as was messaging plumber changed second pump speed up one. That then seemed to prompt ashp to to show play icon solid, pump icon flashing, in turn making top right pipe (in flow from ashp to LLH) to go cold. After a little while panel showed all there logos as usual, fan, play icon, pump (apologies it’s late and forgot what play icon represents).

no change to top left temp. Tried putting left pump to setting 3 still no hot water drawn through. Then out of curiosity though let’s see what happens when hot water cycle runs. So set it to boost on the hot water panel. Instantly top left pipe on LLH went hot.

no idea myself what it means but to my small understanding, got water mode draws heat from ashp through LLH into the system. Soon as that valve shuts and the zone valves open, no hot water gets drawn through (or only a small amount).