Hi again, a funny thing happened today, I cheated the system and made the other thermostat on the manifold call for heat and popped the actuators off the other thermostat and believe it or not the boiler heated to 68 degrees although the thermostat is set to 60, why would cheating the system like that work, I thought a thermostat only told the boiler to turn on and off 🤷🏼♀️😂
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- Thread starter sherylryan
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Are you running the UFH at very high flow/return temps? if not, what are the (mixed) flow/return temps and
what is the flowrate through each loop?
My basic calculations assume that you are using 100M, 16mm loops which will have a ID of 12mm, a 12mm ID pipe will contain 0.113L/M so total of (9+8)x100x0.113=192L in UFH pipework, say another 85L for the boiler+12 rads = total system contents of 277L. Assume max mean temperature of 60C if whole system in service. At 60C, expansion is 1.62%, a 12L E.Vessel with a precharge pressure & a filling pressure of 1bar will result in a final pressure of 2.2bar, if mean system temperature is 55C, expansion 1.36%, then final pressure is 1.92bar. You should be OK IMO, you can see the boiler pressure with a hot system anyway.
| (From water at 15C) | |
| Water | |
| Temp | Exp |
| Deg.C | % |
| 50 | 1.124 |
| 55 | 1.36 |
| 60 | 1.62 |
| 65 | 1.83 |
| 70 | 2.18 |
| 75 | 2.48 |
| 80 | 2.8 |
| 85 | 3.13 |
| 90 | 3.49 |
| 95 | 3.85 |
| 100 | 4.24 |
| 100 | 4.64 |
| 105 | 5.05 |
Strange all right re boiler stat.
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Mixed flow is 48 return is 36/37 on the trouble manifold flow rate is 2.4 lpm per min on 3 loops, 2 litres on 6 loops. When flow meters are opened up fully they never drop to 4 Lpm they only show 3 so not sure if they are reading correctly. Wow you have a lot of knowledge. Thank you very much for all this information.
That loop is emitting 16.1kw, you would think all right that the dT might be less at 2.0/2.4LPM, also still doesn't explain why it takes so long to get the temp up to 50C, the loop contains ~ 90L and assuming a cold water temp of 20C, would only require only 3.2kwh so should only take ~ 10/15 minutes as the loops are emitting very little until the flow temperature rises up a bit. If both UFH+rads on then will be very slow to heat up with a boiler output capped to 26kw, should be OK once rooms up to temperature.
You said the pump is noisy when you try to reduce the head, have you actually reduced it or is it still at 1.8bar?, if you post the other UFH details like above, loop flows+ manifold flow/return temps we can see the total flowrate required (with rads i/s as well) and see if the old pump was/is still suitable.
You said the pump is noisy when you try to reduce the head, have you actually reduced it or is it still at 1.8bar?, if you post the other UFH details like above, loop flows+ manifold flow/return temps we can see the total flowrate required (with rads i/s as well) and see if the old pump was/is still suitable.
Re problem system (again). When you next start it up from cold can you note the individual loop flowrates and the manifold inlet temperature and the mixed manifold and return manifold temperatures especially for the first 10 minutes or so after startup.
The other manifold only has 3 loops going, one at 1.5 lpm, small laundry loop, 2 other loops at 2 lpm. Flow 45 return 40, out of the 15 rads we only run 9 as the remaining are in rooms not used. Forgot mention this boiler also has 24m of trench heating it is suppose to run as well, (we only use this occasionally)
Ok, thanks, you might just post the two manifold pump modes/settings.
What are your intentions now re above?, do you intend to re install the old pump?.
A lot of experienced installers/posters on here reckon that a low loss header is the way to go with systems like yours. I don't have the experience to comment, have only seen one system with a combined UFH&rad system, my daughters, which has run perfectly for the past 9 years without the LLH, she also has a Firebird 26kw boiler with 10 rads and one ~ 120M2 UFH system, boiler has a ancient 6M grundfos selectric running on speed2 and I think the UFH manifold pump is a grundfos UPS2 (but can't see as it & the manifold are hidden).
What are your intentions now re above?, do you intend to re install the old pump?.
A lot of experienced installers/posters on here reckon that a low loss header is the way to go with systems like yours. I don't have the experience to comment, have only seen one system with a combined UFH&rad system, my daughters, which has run perfectly for the past 9 years without the LLH, she also has a Firebird 26kw boiler with 10 rads and one ~ 120M2 UFH system, boiler has a ancient 6M grundfos selectric running on speed2 and I think the UFH manifold pump is a grundfos UPS2 (but can't see as it & the manifold are hidden).
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I believe the pump never needed replaced, the person who installed it use to come out and turn the pump pressure up one week and then the next week he would come and turn it down. This went on for weeks, he turn the pressure up and turned it down. 😂 this afternoon the other manifold had a flow at the boiler of 60 and a return of 59 🤷🏼♀️🤷🏼♀️ After travelling 110m!! Would the trouble manifold need a bypass on it?
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Not sure if I am with you, UFH is generally run at temperatures < 50C, say in the 35C to 45C range, so if the TMV is set to 45C and the boiler stat to 70C, then, initially, all the flow through the manifold will be from the boiler with no recirc, once the boiler temperature & TMV are > 45C then the TMV will start recirculating some of the cooler return manifold water to mix with the incoming, eventually, 70C boiler water to maintain that 45C, IMO, even from cold, the troubled UFH, on its own, should reach that 45C in < 15 minutes at the very most. So question remains, is the temperature taking ages to rise even to this 45C or whatever, there is no reason whatsoever IMO as to why it shouldn't. That is why I'm asking to note (again) from cold that UFH manifold (total) flow rate and manifold temperature rise up to say 45C or whatever the TMV is set to. The troubled UFH TMV is set to index 4.8 (48C??), can't see the other one. If the TMV is faulty and on full recirc then the temperature will never rise but the boiler flow temp will and should rise in a few minutes to its setpoint and the burner should cut out.
What are the two pipe stats controlling?, one seems to be set to 60C. They may be wired as safety stats to stop the manifold pump if the manifold temperature rises too high? or maybe shut the zone valve which then tells the manifold pump to stop.
What are the two pipe stats controlling?, one seems to be set to 60C. They may be wired as safety stats to stop the manifold pump if the manifold temperature rises too high? or maybe shut the zone valve which then tells the manifold pump to stop.
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Our boiler star has been tuned down to 60 degrees by the tradesman to try and stop the boiler from overheating, and he turned TMV up to 48. I keep asking if there is to be a delta t to around 20 at the boiler for it to condensate it’s not going to work as we have already stated with a boiler temp of 60. They turn the TMV up because they want a higher return to make the boiler condensate. The two pipe stats are wired to the pump to stop it incase of high temperatures.
I will let the boiler cool right down and note the times and flow rates. Thank you for all your help.
I can assure you Sheryl that there is absolutely no fear of the boiler overheating even if you run with its max allowable flow temp of 75C or 80C.
Actually the biggest problem with running UFH only is that the boiler return is too LOW, great for condensing effect but bad from a corrosion point of view especially with a OF boiler due to sulphur in the kerosene, problem with a gas fired boiler is that the dT between the boiler flow and return can exceed 30C which is a trip on lots of them. This is one reason for installing a LLH.
On UFH only the UFH return temp IS the boiler return temp.
Example. Boiler flow temp 70C. UFH demand 16kw, UFH flow temp 45C, UFH return temp 35C. The boiler flow (and return) 6.55LPM, 6.55LPM of water at 70C will be mixed with 16.33LPM of recirculated water at 35C to give the required 22.93LPM flow at 45C through the UFH loops.
I will do another calc with radiators i/s as well as UFH.
Schematic may be worth a lot of talking.
Actually the biggest problem with running UFH only is that the boiler return is too LOW, great for condensing effect but bad from a corrosion point of view especially with a OF boiler due to sulphur in the kerosene, problem with a gas fired boiler is that the dT between the boiler flow and return can exceed 30C which is a trip on lots of them. This is one reason for installing a LLH.
On UFH only the UFH return temp IS the boiler return temp.
Example. Boiler flow temp 70C. UFH demand 16kw, UFH flow temp 45C, UFH return temp 35C. The boiler flow (and return) 6.55LPM, 6.55LPM of water at 70C will be mixed with 16.33LPM of recirculated water at 35C to give the required 22.93LPM flow at 45C through the UFH loops.
I will do another calc with radiators i/s as well as UFH.
Schematic may be worth a lot of talking.
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Boiler Flow temp of 60C. Rad output 10kw combined with ufh of 16kw gives a almost perfect boiler return temp of 42.4C which is high enough to prevent corrosion but low enough to give meaningful condensing.
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Hi John, interesting reading and out biggest problem is our troubled manifold is running 70% of the time by itself, where are rads are positioned they receive a lot of solar gain. Our troubled manifold is on a thermostat with a 3 degrees difference to turn back in. The biggest problem is thermostat gets up to temp but with 2 hours the sensor has detected the 3. Degrees drop and turns back on. Where does a LLH go on the system, maybe this is our only option. You are very helpful, thank you.
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