UFH low flow rates

[SamKeen]

Good morning everyone. 
 

I have a problem and I’m hoping someone has the experience needed to suggest a cause & solution.

 

New UFH system installed in our extension. It is running off the house combi boiler (baxi 105he). 

8 port manifold with actuators.

5 circuits are approx 100m

3 circuits 70m 

 

I have 2x 2 port actuators controlling the feed from the boiler - 1 to the old house radiators, 1 to the UFH manifold. 
 

The system is working as it should except the flow rates on the circuits are barely registering 0. As such it is taking forever to warm up the rooms. 

if I close a couple of the circuits, I can increase flow rate on the others, but if they are all open (which is what I need) the flow rates drop to pretty much 0.

 

Is it that my UFH pump isn’t up to the job? See image: 

fyi - boiler is on 2nd floor (2 floors above the ufh circuits and manifold) 

 

[ProDave]

What flow speed is the pump set to (it's off when that picture was taken)

[JohnMo]

Daft question has the system been commissioned and flow rates set.  If not it could be as basic as the flow meters are closed to min setting.

 

Otherwise - Air in system the main issue when you have low flow, your boiler pump and the UFH pump should have enough power to move the water about. My manifold has a pump on speed 1 and is pulling and returning water without issue from the first floor, without assistance from pump on the boiler as well.

 

Assume you had a plumber? If so get him back and tell him to fix it.

[SamKeen]

5 hours ago, ProDave said:

What flow speed is the pump set to (it's off when that picture was taken)

When running the pump is set to the fastest setting (3) not sure what speed that equates to…. 

[SamKeen]

3 hours ago, JohnMo said:

Daft question has the system been commissioned and flow rates set.  If not it could be as basic as the flow meters are closed to min setting.

 

Otherwise - Air in system the main issue when you have low flow, your boiler pump and the UFH pump should have enough power to move the water about. My manifold has a pump on speed 1 and is pulling and returning water without issue from the first floor, without assistance from pump on the boiler as well.

 

Assume you had a plumber? If so get him back and tell him to fix it.

Thanks for the reply. Not sure what you mean by commissioned. There were no air bubbles when I primed the system (cold) before the screed was laid. Then I ran the pluming to the manifold and had a plumber put in the 2 valves. Next to the boiler it’s self so the UFH could work without the rest of the house. 

The flow rates should be around 2.5l/m on the larger circuits. All the flow meters are 100% open. If I close a few of them I can increase the flow on the others. But when they are all open the flow reads about 0.25l/m on each circuit.

which indicates lack of pressure? 

 

do you mind me asking how many loops you have (total approx length) and what pump you have? 
 

cheers guys.
 

 

 

[JohnMo]

Likely the loops or the piping leading to and from the boiler are full of air.

 

How did you connect the UFH to the rest of the system?

 

Do you have auto vent valves.

 

Commissioning is the task of getting the air out the system, and setting pump speed, flow rates for each loop and setting flow temp.

 

I have 7 loops, 3 approx 100m, the rest less than that. Pump is a Grunfoss of some sort, it came with the mixer.

[SamKeen]

I think I have made a simple error. I assumed that the pump would be more than sufficient to run all circuits at max flow rate of 5l/m and it would be a case of turning them down… to get to the design flow temps. I now understand that’s not a possibility - at least not with my pump. 

 

I have just found some old notes of the circuit lengths and they are not as long as I thought and so the flow rates required are massively reduced on the smaller circuits.
 

Utility - 50m = 1.25l/m

En suit - 23m  = 0.5l/m

Old basement zone 1 - 98m = 2.5l/m

Extension zone 2 - 72m = 1.8l/m

Extension zone 3 -  63m = 1.6l/m

Bedroom zone 1 - 74 = 1.85l/m

Bedroom zone 2 - 54 = 1.35l/m

Hallway - 32m = 0.8l/m

so I think… if I correctly set each zone individually… then I should be able to achieve the 2.5l/m required on the largest circuit. 
 

am I on the right track? 

[JohnMo]

Give it a go

[SamKeen]

I’ll keep you posted 👍

[SamKeen]

So I set the red plastic markers on the flow meters to where the internal red indicator needs to get to, and although I can get the right flow on circuits 1,2, 6 and 8, the other circuits are not getting enough. Therefore I’m guessing a higher spec pump is needed? 
 

Any other thoughts? 
 

[SamKeen]

[SamKeen]

[Kelvin]

Your pump is the same spec I had in the last house. Now I don’t know the loop sizes etc as it was all done when we bought the house but it was a fairly large house with a big ground floor. Therefore it’s unlikely to be your pump. That said we did have two separate manifolds each with their own pump running at speed setting 1. Our mixer valve wasn’t set to max either. 

Edited February 9, 2023 by Kelvin

[dpmiller]

Are the heating flow and return plumbed to the correct ports on the mixer?

 

What size of pipe is that at the front left of the mixer?Please tell me it's *not* 15mm...

[SamKeen]

Feed and return are plumbed to the right ports (H & C).
 

Feed and return are 22mm but they reduce to 15 just as they enter the manifold.
 

 I have turned down the mixer to 45 degrees and the flow increases to a suitable level. The rooms are warming up now but the floor itself isn’t warm to touch. Im worked that when I add the floor tiles etc, the system won’t be hot enough… 

 

 

any thoughts? 

[dpmiller]

I think the 15mm sections are strangling the supply to the mixer.

[PeterW]

10 minutes ago, SamKeen said:

The rooms are warming up now but the floor itself isn’t warm to touch

Highly unlikely that it will be - get a laser thermometer to check

[SamKeen]

24 minutes ago, dpmiller said:

I think the 15mm sections are strangling the supply to the mixer.

It’s certainly worth a try. I’ll swap the connections for 22mm. It certainly won’t harm. Cheers mate

[PeterW]

6 minutes ago, SamKeen said:

It’s certainly worth a try. I’ll swap the connections for 22mm. It certainly won’t harm. Cheers mate

Before you do that, try balancing the system using the commissioning caps and not the actuators. Then replace and try again. 

[ProDave]

You don't normally expect UFH to be warm to the touch.  The whole point it is a large area heating the room so only needs to be a little above room temperature.  Anything less than about 37 degrees does not "feel warm"

[Kelvin]

58 minutes ago, SamKeen said:

Feed and return are plumbed to the right ports (H & C).
 

Feed and return are 22mm but they reduce to 15 just as they enter the manifold.
 

 I have turned down the mixer to 45 degrees and the flow increases to a suitable level. The rooms are warming up now but the floor itself isn’t warm to touch. Im worked that when I add the floor tiles etc, the system won’t be hot enough… 

 

 

any thoughts? 

If it’s warm to the touch then your flow temp is probably too high. Think of the slab as a massive radiator therefore it doesn’t need to get that warm to heat the room up. It just does it slowly. Also floor tiles are a good floor covering for UFH. Carpet is the worst as it acts like an insulator. 

Edited February 10, 2023 by Kelvin

[JohnMo]

3 hours ago, Kelvin said:

Carpet is the worst as it acts like an insulator. 

Couldn't agree more. Our bedroom UFH is poor performing compared to the rest of the house. Good job we have the bedrooms cooler anyway.

[Kelvin]

4 minutes ago, JohnMo said:

Couldn't agree more. Our bedroom UFH is poor performing compared to the rest of the house. Good job we have the bedrooms cooler anyway.

Yep. Very obvious in our previous house as the downstairs north facing daughter’s bedroom was the poorest performing too. Our neighbour’s house was a small single storey barn conversion with mono pitch roof. Two external walls facing east and west. Fully carpeted. Less than half the size of ours with similar heating costs. 

 

It’s given us a quandary for the new house though. We are tiling the whole of the downstairs except the family/cinema room which will be carpeted for as much acoustic reasons as anything else. It’s north facing with two external walls and flat roof. In practice it’ll probably be fine especially if I leave the hifi on 😂 

[SamKeen]

4 hours ago, Kelvin said:

If it’s warm to the touch then your flow temp is probably too high. Think of the slab as a massive radiator therefore it doesn’t need to get that warm to heat the room up. It just does it slowly. Also floor tiles are a good floor covering for UFH. Carpet is the worst as it acts like an insulator. 

Cheers guys 

[SamKeen]

5 hours ago, PeterW said:

Before you do that, try balancing the system using the commissioning caps and not the actuators. Then replace and try again. 

That sounds like a good idea aswell. Cheers mate I’ll order some tonight