John Carroll

Can you press (Newheat) pins down to see if they spring back up?, which is I presume what they should do, is the manifold circ pump running?.

@OldSpot will see almost immediately though what effect changing to Auto Adapt does as he can read off the loop flowrates. I have 8 rads on TRVs (old "mechanical" type), I have a 6M Wilo Yonos Pico circ pump where the CP&PP settings can be incrementally changed in 0.1M steps, I have run it for years in PP mode set to 4.6M which gives me the required flowrate of 12.0LPM at a 3.6M head with all TRVs fully calling for heat, the displayed power will then drop from ~ 22W to ~ 15W when the TRVs are throttling down, works very well, havn't adjusted it for years.

Yes, correct, I don't really see though why it should be required or even work on a UFH manifold, where, each system will have its own manifold pump so, irrespective of how many zoned systems are on or off, the flowrates shouldn't change?, why don't you switch over to (CP) Auto Adapt and see what effect it has on yout loop flowrates.

I have never seen any Grundfos Pump working properly in Auto Adapt mode, these had a Auto Adapt mode in PP (proportional pressure) only and generally appeared to run at the lowest PP head which circulated very little through the rads due to the very low head. UFH systems run with a fixed CP head and the loop flowrates are set up manually and are generally fixed, if there are a number of zoned UFH manifolds then the flowrates will probably change slightly depending on the number in service. This is the UPM3 Auto.

Changing the pump mode should result in increased flow, interesting to see if it actually does.

@marshian probably answered your query re continuous heating. You might check the Stuart Turner circ pump mode&setting, it has three constant curve settings and three proportional pressure settings, ensure its on constant curve setting 3, if not sure of the modes, tahe a photo of the pump switch or LEDs while running.

22LPM at a dT of 1C gives a UFH output of, 22*60*1/860, 1.54kW, pretty hopeless for a 11 loop system. Normally one might expect a dT of at least 4C/5C at a flow rate of 2.5LPM/loop even with a low flow temperature, this then gives, 2.5*60*(say) 4.5/860, 0.785kW per loop, in your case, ~ 8.6kW. Increasing the flow rate decreases the dT but should result in a greater output, but something definitely wrong when you are only getting a dT of only 1C. You also posted that when you shut down the GF that the FF flowrates almost doubled with the same dT, this, theoretically doubles the UFH output, can you post the total flow through the GF, can then look at the pump curve, if available, for that 8M ST pump, you might be able to get a suitable circ pump to give you 3.5/4.0LPM. How is the ASHP supplying the UFH, has it got its own pump?

To calculate any UFH output, kW = (total loops flowrate (LPM) X 60 X UFH (flowtemp-returntemp))/860. For example a UFH manifold with a total Flowrate of 15LPM with flowtemp-return dT of 1C will have a output of (15*60*1)/860, 1.05kW.

Have attached two files which combine the UFH+Rads, the other just shows UFH only but you or anyone can play around with the values and you can see the effect, hopefully, more easily. You can configure any one of S.Sheets for UFH only, Rads only or UFH+rads. by just changing the values in yellow. UFH ONLY Sumo Extract Rev0.xlsx UFH + Rads Sumo Extract Rev0.xlsx

No, its the boiler return temperature that primarily determines the Boiler efficiency, the colder the return temperature, the colder the boiler flue gases are, leading to greater efficiency, if you could lower the retur temperature to say 20C then you would have a almost 100% boiler efficiency. The flow through the loops will always and only be greater than the ASHP return flow when the required Loop flow temperature is less than the ASHP flow temperature, for example, with loop flow/return of 36C/26C and ASHP flow/return of 48C/26C, the % ASHP flow is (36-26)/(48-26), 10/22, 0.4545, 45.45%, a loop flow of 7.5LPM will return 7.5*45.45%, 3.41LPM to the ASHP and recirculate/mix , 7.5-3.41, 4.09LPM with the 3.41LPM from the ASHP at 48C to give the 7.5LPM at 36C loop flow temp, (3.41*48)+(4.09*26) = 7.5*36. If, both the flow/return temps are the same for both the loops and the ASHP, then both flowrates exactly the same. The bottom, 4th fom top screenshot below shows this, the 3rd from top screenshot shows the bypass required to give your required ASHP flowrate of 20LPM. The 2nd from top screenshot shows the data if you run with loop and ASHP flow/return the same at 36C/26C and the top screenshot just below shows the bypass required to give that required ASHP flowrate of 20LPM. Hope this is of some help.

No LLH required here (oil fired boiler) the TMV (Tapstat) does the job.

I don't know how how you can reduce the heating loss through the manifold, the only heating loss that I'm aware of is radiation losses which can be improved by insulating the manifolds?, In my (daughter's) case, as long as the water returned to the boiler is less than 40C then it doesn't matter whether like your set up its at 36C or 26C (if you had a conventional UFH where some of the UFH loop outlet water is returned to the boiler. Her boiler has a TMV set to keep the boiler return at 40C, it just mixes some of the boiler flow water with the return water, obviously more HW required if the return is 26C vs 36C, there are also no losses associated with this TMV. For example, if her system had a UFH total flow of 7.5LPM, then its output (and the boiler's) at a dT of, 36-26, 10C, is 7.5*60*10/860, 5.233kW.. With a boiler flowtemp of 54.5C and a return of 36C, then the boiler return (before the TMV) flowrate is 7.5*(36-26)/(54.5-36), 4.05LPM, 1.12LPM of water at 54.5C must be added to give a boiler return flow of 5.17LPM at 40C, if the return is 26C, then the return (before the TMV) flowrate is 7.5*(36-26)/(54.5-26), 2.63LPM, 2.54LPM of water at 54.5C must be added to give boiler return flow of 5.17LPM at 40C, boiler output 5.17*60*(54.5-40)/860, 5.23kW, equals UFH output?. You can see it doesn't matter what the mixing ratios are, same with the UFH mixing. What have you done to improve your own ASP COP? You can theoretically run that at 36C/26C, flow/return with no mixing to improve it, this has nothing to do with the mixing though.

Upnor apparently sell (or did, in 2023) a system something like the subject one and don't even use a TMV, they simply use a Tapstat with some the mixed water also returning to the boiler/ASHP. First screeshot below shows a live system with a ASHP. The manifold pump is pumping Upwards.

The piping diameter will have a huge effect on the pump head required, what is the outside diameter of your loop piping?.

Is that a 6M Pump and has it just 3 settings, what dia loop piping?.

No John, not really, the oil fired boiler here has a TMV to maintain 40C return to prevent corrosion but I've omitted it for simplicity, but I suppose gas fired boilers on UFH only can be run with very low flow/return temps and some can now modulate down to ~ 2.0kW, so some impact here, still it seems a very unconventional way of implementing the UFH and took me a long time to realize that the mixed water can also be used to reduce the UFH flow temperature. I think this schematic might show how this system was running when I noted the data.

Glad to report that after viewing it, I can see that this UFH is operating fine. The manifold pump is pumping downwards, the 3 flowmeters are reading a total of (2.5+2.7+2.5), 7.7LPM, the UFH loops are operating at a dT of, (25.5-19.5), 6.0C, this gves a calculated Boiler/UFH output of (7.7*60*6.0/860), 3.22kW. The downside of this set up is, one, that the mixed water is returned to the boiler and not the UFH outlet water which means that returned water temperature is higher, in this case, returned at 25.5C and not 19.5C, resulting in a slight loss in condensing efficiency, and, two, the manifold circ pump is circulating at twice the UFH loops flowrate resulting in greater pump power required.

Think we can finally put this to bed now as it must? operate like shown immediately below IMO, only difference is that the boiler return water temperature will be the UFH dT higher than the conventional setup plus the manifold circ pump will be circulating almost double the flow. I will post the actual numbers when I see this UFH system. Conventional System

A bit off topic but why are those UPM pumps so popular on UFH manifolds?,

No, it shouldn't, as suggested, the pre charge pressure should be checked first but will require a full or partial system drain down, depending on where the EV is installed, then suggest pre/fill pressures of 1.0/1.5bar.

If its the top of the flow meter(s) is the flowrate then you only appear to be circulating ~ 1.0LPM/loop, 4C seems a very low dT for that very low flowrate. Every 1.0LPM at a dT of 4C will give a output of, 1.0*60*4/860, 0.28kW, 11 loops equals 11*0.28, 3.1kW.

Someone else just pointed out that the bypass is upwards to the valve which does seem more correct as the TMV is close to the UFH manifold pump, anyway the "mystery" to me is solved as its mixed flow temperature water thats returning to the boiler and not the colder UFH return water.

Hopefully, now, 443 viewers can sleep more soundly in their beds tonight, if, as I think the system works this way. It returns the mixed temperature to the boiler, maybe without any 65C hot bypass water or with some hot bypass water if its required to, in the case of a gas boiler, to reduce the dT below 30C and in the case of a condensing oil boiler to avoid low temperature corrosion, some/most oil boiler manufacturers recommend a boiler minimum return of 35C/40C. the TMV, I think is a FM 750 Flow Mix valve, I don't know know if its bypass can be regulated or not, @Nickfromwales or @JohnMo might be familiar with this valve. Ivar Flow Mix.pdf UFH with No TMV Bypass.pdf UFH with TMV Bypass.pdf

Assuming you opt for a 400L cylinder, when heated to 60C and assuming you would prudently leave say 50L after showering then 350L at 60C (and assuming a mains temp of 10C) will allow almost 19.5 minutes showering time for 2 at 15LPM @ 40C or almost 13LPM if 3 showering together, the recovery time to 60C assuming a average coil output of 20kW will be just over 60 minutes or with a average coil output of 25kW, 40 minutes. Probably a "step too far" for you, but a 20/25kW output PHEX would still give you unlimited HW after the 350L is used up.... a continuous flow rate of 9.56/11.95LPM at 40C.