How to get underfloor heating flowing

[Mwhp1986]

I am seriously stuck with an underfloor heating system which isn’t getting warm enough. I have previously had it working perfect in January however is been off a year and now decided no to play ball. I have changed the reliance thurmogaurd mixer which has helped and the manifold is now getting hot but the return isn’t so much. I have flushed all loops out and all seem to flow fine, the upstairs radiators flow fine and get hot, but when it’s just underfloor it just doesn’t get to temperature. I have told the customer to leave underfloor on over night to see how it goes.

 

[ShaunCorbs]

Does it have its own pump ?

 

[Mwhp1986]

Yes mate, grundfos upm3 seems to be working fine but I’m close to changing manifold and pump

 

[ShaunCorbs]

And the flow meters are registering flow on the manifold ?

 

[Mwhp1986]

Yes all of them are registering flow

 

[ShaunCorbs]

What’s the temp coming into the manifold at ?

 

[Mwhp1986]

I’ve only measured the temp of the pipe flow on the manifold and that was getting to 44 degrees

 

[Mwhp1986]

But the flow pipe was red hot

 

[ShaunCorbs]

In theory it’s working should be 5-7 dc difference between flow and return on the manifold eg 44 flow 39/37 return on the ufh pipes

 

[Mwhp1986]

There’s anywhere from 18.5 to 22 deg difference. The boiler is sitting at 88 deg which is high. It’s also circulating through the auto bypass when closing the gate valve I’ve put in it over heats all the time but as the underfloor restricts flow is this normal I don’t think so.

 

[ShaunCorbs]

Yes as you’ve got a difference in flow rates ufh being dt5-7 eg 4x the flow rate of dt20 there should be some separation eg ccts and a lockshield gate valve to balance dt20

 

[Mwhp1986]

Fair one my mind is just mashed from thinking about this for the past 2 days on it. Well it’s being left on overnight so let’s see what happens with it, maybe ambitious thinking but hope it sorts it’s self out

 

[ShaunCorbs]

 

[John.g]

There’s anywhere from 18.5 to 22 deg difference. The boiler is sitting at 88 deg which is high. It’s also circulating through the auto bypass when closing the gate valve I’ve put in it over heats all the time but as the underfloor restricts flow is this normal I don’t think so.

What is the boiler flow temp set to?.

Can you reduce it to 55C which with a normal UFH system with say flow/return of 45C/38C will give a boiler flow/return 55/38C, dT 17C, with no by pass.
If the boiler flow temp was/is say 70c then the boiler flow/return will be 70/38C, dT 32C which will probably cause the boiler to cycle.

 

[Mwhp1986]

at the minute it’s left on full rate to get everything hot but when I go back I’ll be turning it down to 60. I have spoken with the customer and there are only 2 zones that are not heating up at the minute but I need to go back and confirm for myself