Noted.  At least you now have a confirmed route forward and a warm house.  That, in itself, is a step forward however frustrating the wait.  Installer needs to go back to school!

Oh the installed needs to go somewhere, that's for sure! But unfortunately with them contracted by the builder/the BUS etc I've still got some overarching presence of them (ghost of 2 Christmases past now…).

As ever I'll report back on how things go.

My final thought on this, is as it's 48 pages of waffle from me, back and forth.  It would be good to create a summary post, if an admin wouldn't mind - once all is solved.

I could list how conclusions were made, the sorts of things found etc.  In some hope that should this happen to someone, all the mad points are listed (LLH with arrows on back to front etc, strainers blocked, primary circulating pumps, PCB F5 fault, bizarre warranty statements).

And as ever, appreciate everyone's input and suggestions, wouldn't have got this far without them!

Noted.  At least you now have a confirmed route forward and a warm house.  That, in itself, is a step forward however frustrating the wait.  Installer needs to go back to school!

It's likely that I'll need to find my own independent Heat specialist, as not pleased they (installers, builder and specialist) all converse with one another and suddenly out of nowhere get to no availability.

Or just commission a plumber to do the replumbing?

As soon as you touch it your installer will argue that it voids the warranty and I doubt any third party will warranty a system largely installed by someone else (why would they?).  Therefore if you are going to bypass the LLH you have already accepted the risk of a warranty argument (mad I know).  If you are going to do this you might as well cut to the chase and get a regular plumber to change the pipework.

Sorry I didn't explain the situation fully, the agreement was the work would be done with the installers agreement and no warranty void, as they've worked together before (and get advice off him).  e.g. it's "fix this issue" not the entire install is at fault scenario.

I was considering the other option if BUS fails (e.g. our esteemed Government pulls it), but looks like that's going through now in hope if it's pulled tomorrow, our application is in the system…

So now it's a waiting game until next year (again!!)/hope specialist gets a free day and comes over before then.

I have managed to pull the top of the WC down to 42C now the house material seems to be back to a decent state.

So I'm now fully back to where I was before works done on the 5th of November, a situation totally unavoidable had the installer followed the specialist's advice laid out in July.

Least got movement on the BUS (only taken 2 years!)…

It's likely that I'll need to find my own independent Heat specialist, as not pleased they (installers, builder and specialist) all converse with one another and suddenly out of nowhere get to no availability.

Or just commission a plumber to do the replumbing?

As soon as you touch it your installer will argue that it voids the warranty and I doubt any third party will warranty a system largely installed by someone else (why would they?).  Therefore if you are going to bypass the LLH you have already accepted the risk of a warranty argument (mad I know).  If you are going to do this you might as well cut to the chase and get a regular plumber to change the pipework.

Temps were measured across the LLH - specialist saw 3-4C drop with 2 Testo clam meters.  I've looked back at my notes, it used to be 1.5-2.5C with the smaller LLH.

Problem I'm seeing is that the drop (on my cheapo probes) - can range from 2-4C, depending on actual flow temp and how many zones open/shut = will never be able to account for it fully…this might explain my curve had a greater deviance from the Grant default as ambient went up (e..g hotter flow = less drop across LLH, cooler flow = greater drop across LLH) - but I may be coming to a bad conclusion of what I did over that year.

I was running 2C hot since rad uplift fail back in September 2024 through to early this month, so already had a year of 5-6% of increased running costs.  Like you say it's now 12% more (said to builder, I'm in worse state now than before the ill advised LLH upgrade - instead of a volumiser).

Temps have been down to 2C here, and it seems to have held, of course be good to see -3C.

But I wanted to see that without the LLH, not best try W/C inflation…

The specialist highly suspects the primary circulating pump within the Grant ASHP will be sufficient enough to run on its own.  He was thinking (of course) - remove plant room one - as no more LLH (just volumiser), plus remove one at UFH manifold.  He tested unplugging UFH pump, flow rates remained same (another pointless part in this system).

I'm afraid I'll probably be messaging here until I retire about this garbage system…

It's likely that I'll need to find my own independent Heat specialist, as not pleased they (installers, builder and specialist) all converse with one another and suddenly out of nowhere get to no availability.

That - proved that without the temp drop across the LLH (still uncertain why - competing pump rates etc etc distortion, gremlins, no one who's been on site can confirm) - the system could in theory run at system design flow rates with the emitters etc etc to the design of 21C at 40C max flow.

So sort of progress, but...are you certain its going to be OK when it gets cold again?

It's got to point I wonder if people hope I just give in and pay up and live with a compromised system…

Obviously thats the case, it always is!

So now I'm stuck, again, for another winter, running hot.  Now at 44C max flow instead of 42C, as this bigger LLH seems to cause more distortion.

OK well at least you have a warm house.  2C is 'worth' about 5-6% in terms of efficiency, 4C about double that.

Proposal was a temp bypass from ASHP flow to heating zone 2 port valves (turning off the pump room pump, and avoiding the LLH) - to see if in fact, the LLH becomes a volumiser fixes it - without capping/numerous pipe work changes.

Sensible.   

Alternatively just measure the temp drop across the LLH, because for sure thats how much you could reduce your FT if it weren't there.  Of course this doesnt prove that the water pump will suffice whereas the plumbing suggested would.

It's got to point I wonder if people hope I just give in and pay up and live with a compromised system…

Obviously thats the case, it always is!  The installer is now more confident that his hope will pay off because you are now warm!

Assuming you are certain its going to be OK when it gets cold again, the question now becomes, can you hold the installer to the design flow temp.  Thats devil in the detail of the agreement which only you will know.

Alternatively @toodles went to some considerable effort to balance flow rates across his buffer tank to minimise distortion.  Of course this means that it serves no purpose, but we know that to be the case anyway.  You could go down that route, maybe reduce the penalty to 1-2%, at which point its probably best to give up!

Tested system with an inflated W/C of 3.5-4C higher than the installers design.  Rooms got to temp (was slow as house had completely bottomed out).  A little bit of balancing needed mind, but I've said it's on a professional to do that.

That - proved that without the temp drop across the LLH (still uncertain why - competing pump rates etc etc distortion, gremlins, no one who's been on site can confirm) - the system could in theory run at system design flow rates with the emitters etc etc to the design of 21C at 40C max flow.

The next problem becomes - due to all the faffing about, sandbagging, people crossing fingers something would just work and I'd say lets call it a day - the specialist is saying no longer has capacity.

Proposal was a temp bypass from ASHP flow to heating zone 2 port valves (turning off the pump room pump, and avoiding the LLH) - to see if in fact, the LLH becomes a volumiser fixes it - without capping/numerous pipe work changes.

So now I'm stuck, again, for another winter, running hot.  Now at 44C max flow instead of 42C, as this bigger LLH seems to cause more distortion.

It's got to point I wonder if people hope I just give in and pay up and live with a compromised system…

I instructed builder that I no longer wanted the installers on site - as in - you don’t instruct someone else, I will.

Not a situation I wanted to get to, had hoped installers would do the job correctly.

The specialist kindly offered to attend site today as he said he was really worried myself and family this weekend again would be without heating and didn’t think it right, especially with misty conditions and sub zero temp combination being quite hard for ASHP.

So he emptied the strainer again. So seems stuff is still in the system blocking the flow and started to see temps rise again as flow rate shot up. Suspects will have to repeat a few times if flow drops.

He then got his Testo clamps out to check temps across the LLH, and to check actual delta on flow and return with different pump room speeds again to maintain a decent delta and flow rate. And then temps started to rise again more steadily. No champagne yet however. (I know this has time and again been suggested here - just never had the position of someone on site to do it in detail - I probably should have invested in a pair of Testo clamps).

He has 100% confirmed what has been thought here all along, in black and white. This plant room setup loses 3-4C from flow into LLH from ASHP, before gets to heating zone ports. He was a bit surprised in fairness, but it confirmed his July recommendations. I think tbh the smaller LLH had more a 1-3C drop but didn't have accurate clamp meters of course.

He then confirmed at one of the Eskimos the temp seen, and said thinks should they get the actual design flow temp, we’d be seeing 21C temps in the rooms.

I’ve asked him to put a report to the builder which outlays this.

I mean this is not all new, its just from a different position now installer is no longer involved.

My hope is we go ahead with the works and get this finally done and dusted after 2 years.

He even proved the pump for the UFH (so I have one after LLH and another for the UFH) - disconnecting it, get expected flow rates on the manifolds. So that is pretty pointless. So we’re talking rip 2 pumps out, LLH as 2 port volumiser on return only = direct heat to emmiters. Only concern is Grant unit pump if hefty.

I will likely attempt a day of looking at the WC calc doc previously shared here, what the flow temp is on the WC based on ambient temp. And use a fixed flow temp of that +3C or +4C. Then confirm with a probe the rads get the actual flow temp (eg say its -3 outside, flow temp would be 40C, set fixed at 43 or 44C, to account for the drop in plant room, check probe at flow to rad shows 40C) and see if get 21C.

All in all painful it takes 2 years to get here and STILL not got works done that a lot of members said needing doing but contracts etc get in way. I could be here with works done after July report and just be confirming the system works…

In terms of kit I wish I got early on:

(have this recently) Testo 915 - that made it clear to installer, the Heatmiser panels weren’t accurate and forced him to calibrate - £100

2-3x Testo 115i Clamp thermometers (£90 each)

I’d have put clamps:

1 on flow pipe from ASHP in plant room.

1 on return pipe from LLH in plant room.

those two would prove actual delta

then:

1 keep flow pipe location

1 after LLH and plant room pump, just before 2 port heating zones = proof of drop due to distortion in LLH

1 on pipe to radiator in problem zone = proof emitter not getting flow

I think brutally honest having that kit would have removed any notion I’m some mad client with inaccurate probes. They all use this kit.

Thanks James, its honestly hard to keep it together, especially as we’ve slipped into a cold spell. It would have been great to check a fix worked but alas no.

I’ll keep reporting back in hopes that the end fix may help someone here.

Honestly appreciate everyone’s input here. I’ve not ignored it, always relay it to the installers but have been brushed away as some mad client who expects hot rads on a low and slow system.