underfloor heating only works in some rooms

[rb1980]

Hi all, have a wet underfloor heating system. the issue i have is that some rooms/loops work fine and others the floor stays stone cold. new pump was fitted and the supply is hot so no issues there. blending valve set to 45/50 and the flows all read about 2ltrs.
the returns come back luke warm. if i up the flow and crank up the blending temp the return temp is really hot so water is obv circulating ok. what could cause some of the loops staying stopne cold? i have tried running water via the filling and draining loop etc to flush out air and not helped. also one of the loops' flow valve is stuck at a reading even tho the loop is closed and the heatring system is off. when i tried to flush water through that loop it still stayed in its stuck reading.

 

[Agile]

You need to be more scientific with your posting instead of describing "one of the loops" etc.

You need to analyse which loop is which.

A flow gauge is an indication and not necessarily indicative of the real flow.

A professional would give more attention to the flow and return temperatures.

Usually aiming for a differential of about 6 C.

You need to investigate the stuck flow gauge and label each loop and record the flow and return temps.

Tony

 

[rb1980]

ah well i will try to tighten up the temp differecnes then

 

[rb1980]

i think the supplly is like 70 and the return coming back at 45/50

 

[Agile]

I am not sure you are answering the question correctly.

Its the supply coming out of the blending valve which is relevant! Usually set to 45 to 50 C.

Then each loop needs the flow and return temperature to be measured.

That gives an indication of the flow rate in the loop!

It also confirms that the floor is receiving the average temperature between the flow and return temps.

Tony

 

[rb1980]

the blending valve is set to 45/50 as previously mentioned. there is a thermometer in the supply to the manifold pipe as well as the return pipe on the manifold. the supply thermometer reads 70 and the return can be reading 40 degrees sometimes

 

[rb1980]

could the blending valve be faulty? i have read people taking them off and cleaning etc. how is this done?

 

[Agile]

It certainly looks that way.

But even so, the differential indicates there is virtually no flow through the loops. The differential should be about 6 C.

Best to correct the flow through the loops first and then see what the manifold temps are showing. Start at the pump!

Tony

 

[rb1980]

thats great thanks. not to question you or suggest it makes much of a differnce , but have read the diff shout be about 12?

 

[rb1980]

also, what temp should the supply water be at the manifold? cheetrs

 

[Agile]

As I said before usually 45-50 C at inlet to manifold.

The differential is the choice of the designer or installer but I get the impression that most prefer about 6 C as that gives a higher and more uniform heat output.

Tony

 

[rb1980]

tks, what temp would you have the boiler set at?

 

[Agile]

If the boiler also supplies rads then at 70 C.

The blender reduces that to 45-50 C for the UFH.

If the boiler only supplies UFH then it can be set at a flow of 45-50 C on some models. ( Don't do that on most Vokeras though ).

Direct UFH is usually done on the continent. Less often here though.

Often here it is an add on with some rads on the system.

Tony

 

[rb1980]

BRILL TKS

 

[Agile]

When you have an hour or two then read this! But its primarily aimed at the physical installation aspects!

http://www.feeltheheatuk.com/downloads/PEX20_Installation_Guide.pdf


Its also nearly 10 years old and over time different settings to run the UFH are sometimes preferred.