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Discuss How to get underfloor heating flowing in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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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.
 
Does it have its own pump ?
 
And the flow meters are registering flow on the manifold ?
 
What’s the temp coming into the manifold at ?
 
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
 
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.
 
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
 
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
 
 
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.
 
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
 
You might also post the number of zones & loops, the flowrates from the individual flow meters and the manilo;d flow & return temperatures.
 
Well a flow issue is a flow issue irrelevant of how many loops however there are 7 loops for 4 zones with flow rates of 1, 1.2, 1, 0.5 l/m for each zone respectively. As previously stated in earlier in the feed it’s 44deg
 
Well a flow issue is a flow issue irrelevant of how many loops however there are 7 loops for 4 zones with flow rates of 1, 1.2, 1, 0.5 l/m for each zone respectively. As previously stated in earlier in the feed it’s 44deg
Those flow ratate are far too low which is what you mean??, and thats why the returns are so low, they should, IMO, be in the range of 2.0/2.5 LPM, 7 loops at 2.5 LPM = 17.5 LPM manifold flow rate. if the flow/return was say 44/38C then the boler demand will be 9.8kw with a circ flowrate 6.1 LPM with a flow/retur temp of 60/37C, dT of 23C. (assuming boiler SP temp at 60C), The boiler might be happy operating like this?
 

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