John Carroll

Here are the screenshots from your LLH with both balanced and unbalanced primary/secondary flowrates.

Increasing flow rate will have a very small effect on rad output, temperature increase, if possible, is the name of the game, again as said previously, a small increase in flowrate requires a big increase in head which can be very beneficial in balancing rads. You can see, quite clearly below from your set of readings that a flowrate of 20.8LPM with a flowtemp of 59.9C gives a rad(s) output of 16.49kW, increasing the flowrate to 30LPM will only give a 0.96kW increase to 17.45kW, not a lot. IF the flowrate remains at 20.8LPM but the flowtemp is increased to 75C then the rad output increases by a substantial 8.1kW to 24.6kW, if the flowrate is now increased to 30LPM, (flowtemp 75C) then the rad output only increases by a further 1.53kW to 26.13kW. Also, attached, some LLH numbers, for interest. LLH Calcs Extract ET Rev0.xlsx

There's no way a 6.0M or even the "normal" 8M pump will give you 30LPM even with a LLH based on our tests. The Hex loss was 1.54M @ 20.89LPM, this = 3.5M @ 30LPM, The rads loss was 3.9M @ 20.89LPM which will require 8.04M @ 30LPM. Any of the conventional 8M pumps will only give a head of 5.5M ish at 30LPM but the 8M UPS2 which is a giant of a pump at 140W will certainly supply 30LPM and far more at a 8M head, its actually a ~ 10M pump but the "fixed" "CC" speed curves are almost fully CP (constant pressure) curves, no other pump that I'm familiar with will match that performance. If you do think of going for that pump then it might be worth just installing it as a booster pump at minimal installation costs as the boiler circ pump will still have a residual head of ~ 0.66M at 30LPM, enough to avoid cavitation in the UPS2 which requires a minimum inlet head of 0.5M at 75C. The UPS2 other "CC" curves of 7M & 6M can also be useful if the need arises, the LLH can be installed if the above doesn't work out, it's your choice. I will post a few screenshots later of a LLH based on one of your tests to show the effect of balanced & unbalanced flowrates.

Had a look at installing a 6M Wilo Yonos Pico as a booster pump. It should, IMO, provide a modest boost in flow from 20.9LPM to 25LPM or slightly higher, might not seem a lot. but if your problem is getting a higher flow to a few cooler rads then it may be beneficial because the residual pump head now available to the rads should rise from 3.98M (398mb) to 5.7M (570mb), a 1.72M (43%) increase.

Dynamic Head, above should read ~ 570mb, not 510mb.

Their answer(s) is a bit illogical, to me, at least. As stated numerous times before, any control system that is controlling a system that is running under steady conditionds WILL and certainly SHOULD get the process variable (flow temperature) within decimal places of the Setpoint (Target Temperature), and worse, since your flow temperature is apparently being controlled at least > 2.5C above the Target temp then this cuts down the tolerance before the burner trips on overshoot. Again, regarding the maximum 400mb residual pressure setting, this does seem on the low side but now that we know the boiler HEX pressure head loss, (CDI+8000 Chart) its quite easy to see why your system will run at 100% pump speed when set to 400mb. You can see from one of your set of readings, attached, below, that the residual pump head is almost 400mb (398), the pump dynamic head (before boiler HEX loss) is 510mb to give the calculated flowrate of 20.89LPM. I will have another look at installing a second pump but can't see much merit in it just now as it would just reduce (rob) the existing pump's residulal head (when running flat out at 100%) and you could just end up with the same effect as having no extra pump. On 1h35mins Flow 59.9 return 47.8 dT 12.1C Burner 49% 17.64kW. Calculated flowrate, 17.64*860/60/12.1, 20.89LPM Residual Pump Head 400mb OR 100% Speed. ET Rev0.xlsx

Yes, but remember the flowrate is a indicated 21.5LPM at 100% pump speed,a pretty hefty flowrate. If the engineers haven't come and gone please ask them for the boiler HEX pressure loss as I used a assumed one.

Open & shut the pump isolating valves 3 or 4 times, should then hold OK. I have a 6M Wilo Yonos Pico Pump, running fine and silent for the past 7 years.

@EinTopaz I think I may finally have a answer to your query..... " if its 15-70, why is setting 6 (400mbar) show as pump output 100% on the boiler LCD display? Does that essentially mean its got way more head than it's able to use? i.e it's capable of 700mbar, but can only run 400mbar max? I find the manual quite confusing here and it'd be great to understand" The pump appears to be able to calculate the speed required to give a RESIDUAL HEAD of 400mb based on the HEX dP and the system/Rads dP, in your case, with a new clean HEX and because of your system resistance then the pump has to run flat out to achieve this residual 400mb, you can read off the flowrate from the Residual Head chart, which is 20.7LPM at 400mB, the clean HEX dP is only 1.67M at this flowrate. I have based the HEX dP on one I think is correct for your boiler, you might ask them for it sometime.

Did your engineer come back on Friday?

If you are talking about a Immersion then presumably its a Electrical Immersion, if so, the UVC will have somewhere to install this, these immersions have their own integral stats and measure the water temperature where ever they are installed, THe 50%& %75% probes should determine what vol of hot water is used before the HP or boiler is called on to start reheating, HPs might tend to have the probe at 50%, if measuring from the bottom up then the HP might use the 75% pocket.

Below gives a idea of the loss through the boiler HEX, this might be the same as your boiler but try and get the proper one for your boiler. The pump curve above shows that the flowrate (curve A) is ~ 27.5LPM, 1650LPH at a head of 6M, the screenshot, below shows that the boiler HX pressure loss at this flowrate is 3.2M, this leaves a residual pump head of, 6-3.2, only 3.1M, so would require a LLH to allow a secondary pump to suppy enough head to give this flowrate. You could look at installing a booster pump instead of the LLH, far cheaper, even though frowned on by some because a perceived problem that the pumps wouldn't be matched leading to problems, I don't see a big problem with this as pumps like my own Wilo Yonos Pico have virtually infinite head setting (in 0.1M incremants) in CP (and PP) mode, to match the other pump.

If you look at the pump curve above, you will see "H/M" (M is meters) right at the top and it states right at the bottom that H is the Residual head. Residual head is the pump head available after the boiler HEX, you can see the pump head just starts falling, 1200LPM (21.7LPM) @ 7.0M head which indicates to me that the boiler HEX has a pressure loss of 7.0-4.0, 3.0M at a flowrate of 21.7LPM, you are getting very close to this flowrate, 21.5LPM at full pump speed. The residual (remaining) net head of 4.0M is lost through the CH system. If you now install a LLH where the primary pump just circulates through the boiler HEX and a (new) secondary pump circulated through the CH system, then, all the secondary pump head is used to increase the flow through the CH system which will increase the return temp/reduce the dT and get a increase in rad output and a faster warm up. If you install a "6M" secondary pump then the flowrate will increase from 21.5LPM to, 21.5*sqroot(6/4), 26.3LPM, not a lot as the rads dT will only fall from ~ 12C to 10C which only gives ~ 3% in rad output, say a increase of 0.6kW from 18.0 to 18.58. The easiest way to get a faster warm up is to increase the flowtemp to say 75C but would need reducing again when roomtemps reached to maintain reasonable boiler efficiencies. When the engineer next attends ask what the pressure loss through the boiler HEX is, dP & flowrate.

Have you contacted WB re this issue?.