Does air lock affect flow rate in UFH

[Rb1980]

Hi all, having issues with my underfloor heating . Flow doesn’t stay hot as return just stays cold even though boiler is operating as it should . My question is does an airlock reduce the flow rates ? I can get good flow 4+ ltr / min through the loops but still the return and hence flow stays cold . Heated all the radtiors up and then ran the ufh heating this got hot flow to the pump but the temp at the input of the manifold doesn’t get above 40
Any ideas ?

 

[Brambles]

If you have or believe you have airlocks they need to be removed - they will normally stop flow is certain sections rather than restrict it - it all depends on the hydraulic design of the system.

More specifically:

Are you saying that the flow temperature is ambient or 40 degrees C with the pump running? If it is the latter adjust the mixing valve to give 45 degrees ( for a screeded floor), higher for timber. If it is the former, you don't have flow - you either have a blockage or a valve somewhere on the circuit that is closed.

One other possibility is that the radiator circuits are starving the UFH of hot flow. To eliminate this as a possibility run the UFH with the radiator circuits off.

Is this a new problem on an existing system that had worked or are you commissioning a newly installed system? If it is the latter are you sure that the screed was cast with the pipes under pressure and that you don’t have a crushed pipe?

 

[Chalked]

How long are you leaving it on?
underfloor will take up to two days to get to temperature

 

[Rb1980]

Existing system . Flow from the boiler to the mixing valve get to say 60 when the boiler is fired up , out of the mixing valve and into the manifold just lukewarm 40 .
Only had the radiators on to get a good body of hot water to give it a chance to get from flow to return of the ufh . This kept the flow from the boiler to the underfloor hot. Temp at manifold still Luke warm even when rads off
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Update : boiler doesn’t keep up to temp when the ufh is on . Shows 60 when flame is on the shuts off and temps drops to 30 for a bit then the cycle repeats . With 2 radiators on it doesn’t do this so I think it’s some sort of reactriction on the under floor side and it’s makokg the boiler shut off too early . ? But there is flow of 3 l/ m in each of the underfloor loops . Flow temp at manifold never gets above 35/ 40 regardless of if the boiler is fired so maybe mixing valve ?