sharpener

Pumps complain like this when the flow is throttled, maybe the CH circuit is more open than the UFH. Or it might be the ABV opening (assuming there is one).

From this it sounds to me like a control issue that is preventing the boiler from continuing to fire, might be internal to it or external but in view of what you have already done probably electrical not hydraulic.

If you can post a link for the actual product that would be good. Nearest I can find on the web in a quick search is this so I will assume it is something like that. See also this guide. If so it has a pump which boosts the incoming supply and stores the resulting water under high pressure in an accumulator partly filled with air. When it reaches the set point of 3 bar it will stop. The 0.5 bar will be the amount the pressure has to drop before the pump cuts back in, this is to stop it going on and off all the time. The max run time is a limit to how long the pump will run to try and refill the vessel up to the set point. I am surprised it ever takes as long as 3 hours, that is a flow rate of only 1 litre/min so it must be really struggling for water. I am assuming it works on cold water only so I am guessing the high temp limit is a measurement of the motor winding temp to prevent it burning out, I am not surprised this is triggered if it is struggling. The stored volume of water is only 174 litres so that is the max you can get out at the boosted pressure, which should be enough for maybe three 5 min showers, after that you will only get the flow rate that the pump can manage from the mains alone which is very feeble. You could try increasing the set point as much as you can before you get to the 4.5 bar h.p. warning level to give you the maximum storage volume. The 0.2 bar is a warning level, presumably the pump needs at least this on the suction side to function correctly, so you do not have this all the time. However if the pump is up in the attic with the rest of the plant and the incoming mains pressure is only 1.1 bar (is that static or with any flow and if so how much?) then it can only lift the water to a height of 11 metres. If the mains pressure is not sufficient at a reasonable flow rate to get the water high enough for the pump to be able to function properly without cavitation the pump will struggle to pressurise it any further, I think this is likely to be what is happening. Check what suction head the pump is designed to achieve. In which case the solution is to re-install the pump (or a different pump) at ground floor level so it is flooded on the suction side and will perform better. DAB pump sets are I think well regarded, comparable with or better than Stuart Turner IMO, but the one in yr link works differently. It has a tank storing 500 litres at the incoming mains pressure and then a pump to provide the supply to the house. If you want 3 showers at once you need (a) enough stored volume (b) sufficiently large diameter pipework to minimise pressure drop and (c) enough pressure, 3 bars should be adequate as that is what unvented cylinders usually work at. This DAB pumpset will provide 80 litres/min at 3 bar so enough for 4 rain showers at once. But it relies on the mains pressure to fill the tank to begin with and so could not be installed in the attic if the underlying problem is that the mains pressure will not lift the water that high, and it will not solve the problem.

I think these are part of the problem. (Also the low UFH return can starve the rads but it sounds like it is not this.) However 16kW sounds a bit low, we have a 180 sq m barn conversion with uninsulated stone walls and 12kW is absolutely on the limit for about half the floor area. Was it always like this or is the lack of performance new? If you had it put in in 2022 it is less than 3 years old so what do the original installers say? If all else fails you could pay for a Heat Geek qualified engineer to take a look and make recommendations.

@JohnMo will be along to tell us soon enough. If he needs to come back ask him to tell or show you, then you will know for sure.

Can you not see the pressure on the FTC6? I am a bit surprised your Ecodan will start up with zero system pressure, my Arotherm plus won't hence my discovering the EV problem in the first place. But no pressure measurement will tell you what the proportions of air and water in the vessel are. And you cannot achieve the correct pressurisation of the vessel without letting the system down to atmosphere first to ensure it is empty of water, did your "engineer" do that?

Might be wrong pressure setting in the expansion vessel. My installers left it at factory 3 bar setting so it wasn't accepting any expansion volume and the pressure fluctuated a lot. Solution was to let the system pressure down to atmosphere, then let the EV precharge down to 1.2 bar, then pressurise the system back to 1.5 bar which leaves 4/5 of the volume available for expansion.

Avoid buffer if you can. I have a custom thermal store with an internal baffle but the results are disappointing as the two volumes mix to a much greater extent than I was expecting.

Some ppl are prepared to use battery for arbitrage between the 5p on Cosy off-peak and their Fixed Export at 15. Depends if the warranty is on elapsed time or number of cycles. Might think about it later in the spring when I don't need all the storage for the HP.

16mm^2 cable is what was formerly used for meter tails on a supply with an 80A cutout. But 25 mm^2 meter tails and 100A cutouts are now standard so at first glance it might not be thought to be enough. However for charging you will almost certainly be OK as 80A at mains voltage will in theory allow you to charge a 48V battery at nearly 400A (neglecting losses). For discharging it depends on the inverter rating and topology, I assume you will locate the inverter in the plant room to minimise losses. The existing cable will handle anything up to 18.4 kW; in a domestic setting you would be more likely to need 8 or 10 kW at most. We have a Victron 5kVA and it is fine for nearly all purposes, and 10mm^2 is adequate for input and output as even in pass-through mode it is limited to 50A. Whether you need to run a second cable also depends on the inverter circuit topology. With a Victron you could get away without it by wiring everything to its AC-In terminals but that is a bit unusual, separate inputs and outputs are more the norm. You might also think about other heavy current users like HPs and EVCPs which have their own particular wiring requirements. And also putting in cable runs for the various current transformers needed. Maybe a duct would be better if you don't yet know what you will be needing. Earthing is a whole topic in itself. Many Chinese inverters are not compliant without extra kit.

Don't see why not subject to DNO approval. Not sure if DNO needs MCS for battery, mine didn't, was self-installed. However in getting the Octopus export tariff the MCS cert does save the £250 fee and maybe loads of aggro, see this thread. My second array of panels is wired in to the 48V battery via a charge controller, so the installers said they couldn't provide an MCS cert as it has to have an AC meter serial number. A brief discussion about the balance due on completion resulted in a swift change of heart and certificate with the number off a random meter still in their stores. Would be surprised if your typical conveyancing solicitor is sufficiently clued up on what paperwork is appropriate for the electric house with all mod cons, solar PV, battery, heat pump, EVCP etc.

Lots of discussion over on here, users I think are mostly satisfied.

The typical killer is the 22mm pipe to the bath. Make sure the washbasin taps are piped separately all the way from the tank in 15 or even 10, then you won't need secondary recirculation or pumps or stats or timers which can all go wrong.

Tubular heaters sold for e.g. greenhouses? Low output per unit length though. Yes I remember a whole variety of heaters of yore. My parents had a vertical cylindrical Belling convector ?1kW which was styled to mimic the old paraffin heaters, that had no thermostat. And two rectangular convectors by Morphy Richards, one had a thermostat and one with no controls of any kind. All three had comfort lights which shone an orange glow downwards on to the floor. My grandmother had a single bar (1 kW) fire where the grill was vestigial and it was easy to touch the element. At Coleton Fishacre (NT place in Devon) there is a wonderful Art Deco fire in the shape of a yacht, the completely unprotected rod element is the mast and the chrome reflectors are the sails!

Make sure he leaves the HP truly level front to back, as if not the fan bearings will wear prematurely. Side to side is more noticeable - but less important.

It's quite difficult to optimise even for a single installation and there is certainly no "one size fits all" solution. Yes, I suppose I was assuming a best case scenario with smart meter, metered exports and maybe batteries. In which case even if I was generating sufficiently I would not be running the dishwasher and tumbler dryer now bc I would be consuming PV that would otherwise be exported at 15p. Whereas if I run them 0400 - 0700 they cost me only 5p/kW. This is why I was keen to get the 3.7kW export limit removed as I had no good way of predicting the daily PV total or making sure I was charging the battery with the 3.2 kW surplus rather than simply have the PV generation curtailed. OTOH it is still worth making sure my battery is fully charged 1300 - 1600, bc the stored energy displaces consumption from the grid later in the day at 25p/unit.

The two are not really connected. If you can avoid the peak rate by time-shifting your usage then using say Octopus it can be better to export at 15p when you can and import at 12p when you need to. Unfortunately at this time of year there is no chance of PV when you most need it, during the evening peak 1600 - 1900. And although the best generating time is often after lunch, home consumption is only saving you 5p/unit then as that is the Cosy cheap period 1300 - 1600.

Not summer and winter grade, they are different products year-round. 28 sec or kerosene is used in most domestic oil boilers. (And paraffin lamps/heaters. Is also basically the same as AVTUR for jet aircraft engines.) 35 sec oil or "red diesel" is used in a few boilers (we had a Potterton which did), also farm vehicles which is why it is dyed as it is taxed at only 5% and illegal to use for road vehicles. And previously used for most recreational boat engines though IIRC it is being phased out and they will have to buy (taxed) road fuel diesel in future. This is misleading as MCS installers will not quote for flow temps above 45 or 50C at most, so you will in practice be lucky to find one who won't require upgraded radiators (mine by a factor of 1.9x). £295M will only pay for 40,000 grants though which is a drop in a bucket. Total BS greenwash and waste of money. The same savings can be made at much less cost by replacing fossil fuels in static applications, road vehicles or (less easy) shipping.

Starting to look like a real problem. We are less than 200m from the sub-station and regularly see more than 250V. If you are curtailed bc of high voltage at your meter presumably the DNO would have to do something about it. If however the issue is voltage rise between yr meter and the inverter then I guess you would have to install fatter cables and pray.

With the current tariffs available it may make economic sense to export all your production rather than self-consume. In that case it does not matter if the array is not optimised for year-round output or peak winter output. From the point of view of the planet it might be better to incentivise production in winter but (a) that hasn't happened yet and (b) it is usually so low at this time of year it would not make a lot of difference in the grand scheme of things. So better to have any kind of panels than none at all.

@Chanmenie implied the buffer was external whereas the linked article says it is inside the outdoor unit. I suppose it might depend on the size, there will be more free space in the 15kW version with its bigger fan and evaporator. But again you would not expect the one size - 16 litres - to be appropriate for all models.

No, none whatsoever. The rad sizes and positions are now set in stone. This philosophical discussion was all a fork from the original thread caused by this enquiry: The only changes I am wanting to make now are to do with stopping the UFH from preventing the rads running at their design flow temp. Today I have been making a series of measurements but paradoxically the OAT has been 8.5C so the o/p of the HP is more like 15 or 16 kW and the problem is hard to replicate under these conditions.

Sounds plausible and explains why it only needs 16l tank. But this is for defrost, and as upthread antifreeze protection is a different beast. None of this will protect the hp if there is a power cut and you are away so I do not understand how Viessman can say they need neither AFVs nor glycol.

This has all drifted a bit off topic, but the formula is quite well known and quoted above. (65/50) ^ 1.3 = 1.406 (20/50) ^ 1.3 = 0.304 so it is fairly clear that is what they have used. In my case the design is for a bedroom @18C with a MWT of 47.5 so the correct factor is (29.5/50) ^ 1.3 = 0.504 which is pretty close to the installers' 1/1.9. Also they have not taken a/c of the heat flux from the kitchen below. The major problem is distribution not production. The cold comes from the window wall which is the only external wall, the heat comes from the rad on the opposite side of the room. No, a fan of any kind would not be acceptable to OH (whose study this is) bc of the noise.

When all else fails an old-fashioned analogue multimeter is your friend.