New member with an underfloor heating issue

[Jon C]

Hi all, long time lurker but now a registered member. I've found this to be a fantastic resource for helping with projects and troubleshooting about the house. I've noticed that one of the loops on my ground floor Emmeti Topway UFH manifold (I'll call it loop 1 as its the first loop after the pump - pic attached) is not getting warm on the return side even after being on for a long time at max flow. The other two loops get warm fairly quickly. I've found that shutting loops 2 and 3 off, loop 1 will get to a max if 4 l/min with the flow meter wide open. The other two will bottom out the flow meter (>5l/min) opened wide with the other two shut down. Doing this experiment I can hear the automatic bypass valve in the system is letting by when just loop 1 is full open, whereas if just loop 2 or loop 3 is wide open then it's quiet and not allowing flow through suggesting that loop 1 is restricted compared to loops 2 and 3. I've had the actuator off to test if the pin being depressed stops the flow, which it does. This says to me that water IS moving all the way through the loop. I've come to the conclusion that the loop is air locked, not blocking flow but significantly reducing it. Thing is, if the flow meter is saying 4l/min, wouldn't that be sufficient to feel warmth in the return pipe? Or is it the case that if the loop is air locked the velocity of the water is high going past the flow meter paddle but getting severely restricted further along the pipe where the air is. Or am I barking up the wrong tree with the air lock hypothesis? Any help would be greatly appreciated. I'm not sure the loop in question has ever worked properly since we've lived in the house so it would be a good feeling to get it working.

[dpmiller]

sounds like air OK, and you'll probably need mains pressure to shift it...

[Jon C]

Thanks @dpmiller  I thought I'd likely need to get the hose out! Thing I'm worried about is my unvented cylinder has a 2.1 bar prv and all the cold pipes in the house come off after it, including the outside taps. Do you think 2.1 bar will shift it?

[Temp]

I think its more about getting sufficient flow rate to shift it rather than the pressure.

 

Consider putting some corrosion inhibiter in the system while you're at it. Check the amount needed on the instructions as you may need a few bottles. My system needs something like 3 * 500ml bottles. 

[Jon C]

Thanks @Temp. I'll be giving it a go and hopefully it is as you say about flow rather than pressure. Good point about the inhibitor. How did you go about getting the inhibitor into your system? I've read that people often do it at a radiator but I'm UFH throughout. I've only recently added flow meters to my manifolds and was happy to see that even after 10 years, when they filled the water is clean so it was either treated approptiately on commision or as i'm UFH throughout and its plastic pipe and brass manifolds it's not much of an issue. When I've had a leak on a manifold before it's had a chemical smell but I assume it's glycol as it's heated via ASHP. I guess if I'm flushing out a loop plus the flow and return bars, I ought to at least top up with inhibitor and glycol... but how's best to do it? ?‍♂️

[Temp]

Our UFH ystem is unpressurised so easy to put inhibitor in via the header tank.

[Jon C]

Hi @Nickfromwales. I've noticed you're  Guru when it comes to UFH. Would you mind casting your eye over my issue please? Would you agree that it's likely air in the loop? And how would you advise i add glycol and inhibitor back in after a flush through? I'm a fellow Welshman, grew up in the Vale of Glamorgan, now living un Surrey though ?

[Jon C]

Got the hose out today and flushed my problem loop. No joy with improving flow rate unfortunately ?. Flow meter showed 4 l/min during flush and the water coming out the drain hose looked like 4l/min or less (didn't measure) despite a flow rate going in of around 10 l/min. The water coming out was blue initially but eventually was clear after a bit suggesting that I'd exchanged all the antifreeze treated water in the loop with fresh water. I left it running for about 15-20 mins if not more. Tried depressing the valve pin and releasing it suddenly to try and stimulate a release of the "restriction" many times. I'm stumped now. It seems there is a restriction limiting the loop to 4 l/min even under my mains pressure. As an aside, when finishing the flush, I shut the drain valve off with the fill still open and hose running and the new gauge showed 1.7 bar. I have an unvented cylinder and the prv is set fixed at 2.1 bar so i was surprised that it only came up as 1.7 bar. I was wondering there is a leak as initially on closing the gauge was closer to 2 bar momentarily and then came down to 1.7 over a few seconds. But it was then stable at 1.7. Guess I should check my mains pressure directly at the tap in case the prv is in need of cleaning/replacement. Anyway... I don't know whether my mains is too weak to shift the restriction (whatever it is) or whether the restriction is un unmoveable. I've considered that if the restriction isn't air and just a constriction then 4 l/min is ok. If it's air then heat transfer is affected. I left the zone running for a few hours today and the floor went from cold to slightly warm in the zone which is an improvement. I wonder if despite not removing the restriction, some air was purged and heat transfer has improved. Return pipe still doesn't get warm but I figure its only 35 degrees going in (ASHP in eco mode) and it's probably all going into the floor. My next step is to try swapping actuator pin with another zone to see if the pin valve is the restriction issue. ?

[Triassic]

On my set up I found that the flow indicator on top of the manifold had been screwed in to far. Remove the red cap and unscrew it a turn or two and see if this helps.

 

Google - Manifold flow setting

Edited October 10, 2021 by Triassic

[Jon C]

Thanks for the suggestion @Triassic. Had a tinker but no joy. Glad you got to the bottom of your issue though!