John Carroll

There's a big difference in output between running a rad with a flow temp of 40C and a T40 rated rad A T50 rated rad (now the standard) often has 75C/65C/20C printed on the top of its spec sheet, is the mean rad temp - the required room temp, the mean rad temp is the (flowtemp+returntemp)/2 and 20C is the most often quoted required room temp, so the T50 rad above is ((75+65)/2) -20, 70-20, 50C, a T50 rad. A dT of 10C will require a flowrate of 1.43LPM/kW If the flowrate is kept the same then a T40 rated rad will have, flowtemp/returntemp/dT/output, 63.73C/56.25C/7.48C/74.8% but if that rad is run with a flowtemp of 40C (same flowrate) then these numbers become 40.0C/37.23C/2.77C/25% A T25 rated rad numbers are 47.03C/42.97C/4.06C/41% but if run with a flowtemp of 25C then these numbers are 25.0C/24.53C/0.47C/4.7%. One might thik that a T25 rad would give 50% output, (25/50)x 100, but it doesn't, it gives (25/50)^1.3 x 100, 41%, similarly a T40 rad will not emit 80% of a T50 rated rad, it gives, (40/50)^1.3 x 100, 74.8%

Thanks, did/can you do the pressure gauge checks and the flow rests.

Try and do this please . Typical Pumped Installation below

Suggest cleaning the Y strainer and removing the two pressure gauges, (ensure they then read zero pressure) ensure tapping points clear then replace them. With pump off run a "high" flow hot tap only, like a bath tap, if installed, run the hot tap into a bucket/container for exactly 30 secs, measure with a 1 litre milk bottle or whatever, X by 2 to give the flow rate in LPM, note the two pressure gauge readings before and during test. Then start pump with tap still open, throttle the tap flow until the pump pressure is close to 2.0bar, then again note repeat the flow measurements, again note the two pressure gauge readings before and during test. That should/might give enough information on how to proceed.

I estimate that you have a 300L accumulator, A precharge pressure of 1.4 bar and a charged pressure of 2.2bar will give a available accumulator vol of 75L, two taps running for 15 mins to use up this 75L gives a combined flowrate of 5.0LPM, (not a lot). It took the pump 37 minutes to recharge the accumulator with, theoretically, 75L, gives a pump flow rate of 2.03LPM, no good. Have you any idea of the flowrate from those two taps before the flow rate fell off. Its very difficult to tell whats happening without a accurate schematic of the pipework. You will see a round plastic dust cap right on the very top of the accumulator, unscrew or prise this off and you should see a (schrader) valve exactly like your car tyre valve, you require a tyre type pressure gauge to check this pressure with the accumulator fully drained. Before considering doing this, or getting it done, with the pump running and no water demand, press down the (schrader) valve pin with your finger nail, if air comes out, diaphragm OK, if water comes out for more than a few seconds then diaphragm knackered.

Double post.

The above temperature is 1/2 way up the tank. Does this temperature probe also control the heat pump/heating coil on/off?, normally the cylinder stat/control probe is installed say 150mm or so above the bottom of the heating coil, then depending on the coil dT (which depends on the flowrate etc) the temperature at the cylinder top might be ~ 10C higher than at the "bottom" so maybe 5C or so at mid point but if the control is from midpoint then less of a gradient. where are the coil inlet/outlet connections? and what is the HP flow/return temps and flowrate with cylinder heating only on?.

Will read back the posts sometime but was that H actually opened up?. A relatively small system leak could also cause these problems with sludge etc but would require tying up the ballcock on the F&E cistern for a day or two and then see if there is makeup when released. I have a isolating valve on the make up and only open it every few months for a min or two to check for leaks.

Well, I think what I have learned from this thread is that the first port of call should be to ensure that the vent is installed properly, ie, up and over the cistern, even with a perfectly clean H there was bound to be some carry over and aeration with that installation, there are literally dozens of houses around me, some, with the combined cold feed and vent and some with the H, some have never ever had a drop of inhibitor since these houses were built, over 50 years ago, yet some have rads, like my own, 30 and 40 years old. I can only assume that no air is ever entering the system(s) and obviously no system leaks.

All because the vent wasn't carried up and over the F&E Cistern originally?.

Presume the pump discharge is teed in above this PRV, otherwise the accumulator will only run at 1.5bar, useless, with a precharge pressure of 1.4/1.5bar?., where would/should a check valve be installed?.

I only saw this photo today. Can you switch off the pump and open a few taps to give a good flow ~ 15LPM and note the two pressures, switch on the pump and note the pressures again, shut the taps and note the pressures as the pump stops. Also check to see where the pump discharge (outlet) pipe is teed in to the system.

"Also check for a schrader type valve (like a car type) on top of the accumulator, if there is one, check that pressure with the cylinder fully drained, it should be at or set to whatever D7 is set to (Charged pressure - 0.2bar)." Should be set to the precharged pressure, D7.

Simply put, yes, the specified T60 rad output should, IMO, be 643/0.17212, 3736 watts. Don't know what the corrected loss of 2074 watts means though.

No problem. First, you know yourself what the minimum pressure you require to give you the minimum acceptable flowrate, so change (cell) D16 "End Pressure" (present setting 1.5bar) to whatever the minimum operating pressure is or should be. Then change D7 "Precharge Pressure" to the D16 setting minus 0.2bar, if you set D16 to say 1.8bar then set D7 to 1.8-0.2, 1.6bar. Change D9 & D18 (both) "Charged Pressure" to whatever your pump is cutting out at, present setting, 2.2bar OR whatever you think it should be capable of. D6 "Accumulator Capacity" present setting 175litres, leave or change it to whatever the actual capacity is, if not known, get a tape and measure the circumference, and the height, post back and a good estimation of the capacity can be arrived at, also state the insulation (if any) thickness. Also check for a schrader type valve (like a car type) on top of the accumulator, if there is one, check that pressure with the cylinder fully drained, it should be at or set to whatever D7 is set to (Charged pressure - 0.2bar).

I would get that pump looked at for a start. If that was operating as designed then it should have no problem in achieving 3.0bar could give a 71% increase in the accumulator output, refilling time for a 175L accumulator should still only be 11 ninutes or so. Accumulator 175L Calcs Rev 0.xlsx

What I have all ways used based on the mauufacturers correction tables for mild steel rads at any rate is the exponential 1.3. A 15.5C rad will have a correction factor of (15.5/60)^1.3, 0.17212 to give 285.894 watts from a 1661 watt (T60) rad, or 96.16% of your figure of 297.32 watts.

Yes, the calcs are correct. Its a bit strange though that the rad outputs were based on a T60 rating which was replaced well over 10 years ago by the T50 standard in the UK, if the rads are actually "T50" then any calculated output(s) based on T60 will be 20% or so lower, shouldn't affect the UFH though. Might also be worth checking the flow/return temps in the bathroom rad to get a proper dT, it may be far greater than 3C.

Just looking at the figures for the bathroom, flowtemp of say 39C with dT of 20C? gives a return temp of 19C, a mean rad temperature of, (39+20)/2, 29C, giving a output (T60 based) of ((29-20)/60)1.3, (9/60)^1.3, 8.5%, rad output, 5668*8.5%, 482BTU by my calcs or 141W (not a lot), if the room temp is 18C then the output is (11/60)^1.3, 11.02%, actual rad output 5668*11.02%, 625BTU, 183W?. That dT seems very high for a flowtemp of 39C, would have expected ~ maybe around 8C or so which would increase the rad output due to the higher mean rad temp so ~ rad output of 16.49% to give a output of 935BTU, 274W assuming the room temp rose to 20C.

This is probably very similar to your pump, your pump has a higher closed valve head of 3.98bar. It should really have no problem in reaching a cut out SP of 3.0bar when the demand finishes, as long as the inlet pressure is > than 0.7bar. How long is it running for before it cuts out at 2.2bar? You might also measure the accumulator circumference with a tape, can then get a good idea of its capacity at 6ft? high.

A few basics about any accumulator. Its important that the precharge pressure (air end pressure with no pressure at the water end) is set to just slightly less than the minimum required pressure, if, for example, the minimum required pressure is 1.5bar, then the precharge pressure should be set to 1.3bar, if the pump SP pressure is set to its design? pressure of 3.0bar then the available water vol per 100L of accumulator capacity is 34.5L, if the precharge pressure, for whatever reason is set to only 0.5bar then the available water vol in falling from 3.0bar to 1.5bar is only 22.5L, important to bear this in mind. You have the pump SP at 2.2bar , assuming the precharge pressure is 1.3bar then the available water vol in falling from 2.2bar to 1.5bar is 28L (per 100L of accmulator vol), I would definitely suggest checking that precharge pressure and set it slightly below your required minimum pressure and reducing the diff to 0.8 bar, as you suggested, Can you also post the pump inlet and outlet pressures with a big demand. Also the the indexed setting in the window of that ABV?, automatic bypass valve, located between the two pressure gauges.

What is the continuous HW flow?, just run that same HW bath tap that gave you the "accumulated" 28LPM but don't take a flow reading for say 8 to 10 minutes, or until the flow dies down, to ensure no boosting from your EV. For interest a (mains only) accumulator filling pressure of 4bar and a "user" pressure of 3.0 bar will provide 20L per 100L in falling from 4.0bar to 3.0bar, other numbers, 4.0bar to 2.5bar = 30L. 3.5bar to 2.5bar = 22.2L. 3.5bar to 2.0bar = 33.3L. 3.0bar to 2.0bar = 25L.

I reckon the boiler efficiency changes by ~ 4.5% for every 100C change in fluegas temperature.

OK, you will see from one of my previous posts that assuming the wet gas loss is 10% that this results in a condensate vol of 0.1595L/kWh of consumed gas,( "confirmed" more or less by @Bornagains calculation). From your data, gas consumption was, 544.539-544.019, 0.42m3, assuming 11.0kWh/m3, consumption was, 0.42*11.0, 4.62kWh, IF fully condensing, then condensate vol, 4.62*0.1595, 0.7369L, 0.7369*1000, 736.9g, actual condensate (collected), 612g, 612/736.9, 83.05%of max condensing, so condensing effect 10*0.8305, 8.31% (slightly higher than original calc), overall boiler efficiency, 88.8+8.31, 97.11%. "Meter reading at start 544.019 m3, Meter reading at end 544.439 m3. Condensate collected 612 grms"

But your boiler efficiency is still ~ 97% (as per graph, above), at say 30C fluegas temp, with a OAT of 4.1 C you are losing ~ ((30-4)/100)*4.5, 1.2% sensible heat to give 88.8% + the condensing effect, not quite the full 10% but by my calcs, 8.29%, to give a overall efficiency of, 88.8+8.29, 97.09%, TG it didn't come out at > 100%!!.