Underfloor Heating Unexplained Temperature Drop

[swiflee]

Hello all,

Underfloor setup is as follows:

Dedicated 22mm flow from 2 port valve
Dedicated 22mm Return which tees in to 28mm by cylinder.
11 Port Manifold
Grundfos 25-60 Alpha 2 pump on manifold.
Heatmiser setup but nothing is wired in as yet.


The problem is that when the pump is off, the flow and return get hot and the temperature guages on the manifold top bar and bottom bar read 40ish degrees and the manifold bars get hot to touch indicating water is in there.

As soon as the circulator pump is switched on, the temperature drops straight down to 20 on both manifold bars and the 22mm return to boiler cools down.

We have done the following:

1) Replaced thermostat head.
2) Checked non return valve is operational
3) Checked that pump is spinning clockwise and installed the correct way.
4) Checked pins are free to movement on both return and flow and all caps are off on the manifold return loop.
5) Checked the UFH 2 port valve is set on manual.

Both heating engineer and manifold manufacturer are at a loss as to why this would happen so am asking here in case there is any expertise that you may be able to share?

I would have expected the "boiler temperature water" to flow around the loops with a temperature drop on the return indicating that heat has gone to warm up the floor?

Cheers

Fred

 

[tolly]

Hello all,

Underfloor setup is as follows:

Dedicated 22mm flow from 2 port valve
Dedicated 22mm Return which tees in to 28mm by cylinder.
11 Port Manifold
Grundfos 25-60 Alpha 2 pump on manifold.
Heatmiser setup but nothing is wired in as yet.


The problem is that when the pump is off, the flow and return get hot and the temperature guages on the manifold top bar and bottom bar read 40ish degrees and the manifold bars get hot to touch indicating water is in there.

As soon as the circulator pump is switched on, the temperature drops straight down to 20 on both manifold bars and the 22mm return to boiler cools down.

We have done the following:

1) Replaced thermostat head.
2) Checked non return valve is operational
3) Checked that pump is spinning clockwise and installed the correct way.
4) Checked pins are free to movement on both return and flow and all caps are off on the manifold return loop.
5) Checked the UFH 2 port valve is set on manual.

Both heating engineer and manifold manufacturer are at a loss as to why this would happen so am asking here in case there is any expertise that you may be able to share?

I would have expected the "boiler temperature water" to flow around the loops with a temperature drop on the return indicating that heat has gone to warm up the floor?

Cheers

Fred

Is the 2 port valve energised or is it manually hooked open, if the 2 port is hooked open and the boiler is running for HW or a rad circuit, you will get some heat at manifold even if the manifold pump isn't running as it can circulate around the mixing valve.

 

[jonnyswamp]

When u/floor pump is turned on (and I pressume boiler is firing) does flow to mani get hot
What temp is boiler set at
U/floor returns will take a while to heat due to design (heat loss into floor) and length of circuits
Get it wired up correctly first, then try again

 

[swiflee]

Is the 2 port valve energised or is it manually hooked open, if the 2 port is hooked open and the boiler is running for HW or a rad circuit, you will get some heat at manifold even if the manifold pump isn't running as it can circulate around the mixing valve.

Is the 2 port valve energised or is it manually hooked open, if the 2 port is hooked open and the boiler is running for HW or a rad circuit, you will get some heat at manifold even if the manifold pump isn't running as it can circulate around the mixing valve.

All 2 ports are hooked open at the moment. The 3 rads circuit runs great and you can feel the UFH flow pipes get hot, and the manifold. But as soon as the circulator pump goes on.....

 

[swiflee]

When u/floor pump is turned on (and I pressume boiler is firing) does flow to mani get hot
What temp is boiler set at
U/floor returns will take a while to heat due to design (heat loss into floor) and length of circuits
Get it wired up correctly first, then try again

Yeah flow to mani gets hot when pump is off / boiler on.

Boiler set at 50 Degrees atm and permanently on at the moment.

I expect a drop on the return but I am seeing the drop on the flow temp.

 

[tolly]

All 2 ports are hooked open at the moment. The 3 rads circuit runs great and you can feel the UFH flow pipes get hot, and the manifold. But as soon as the circulator pump goes on.....

when you say as soon as the ufh pump goes on....what do you mean,

does both the flow and returns go cold, or just the return, as said its normal not to be able to feel any heat in the return loops when first turned on.

do you have flow meters on the manifold?

 

[tolly]

what temperature is blending valve on manifold set to aswell?

 

[swiflee]

when you say as soon as the ufh pump goes on....what do you mean,

does both the flow and returns go cold, or just the return, as said its normal not to be able to feel any heat in the return loops when first turned on.

do you have flow meters on the manifold?

Pump is running directly on the mains atm just so we could test system. The flow cools down and the return goes cold when the pump goes on.

Yes I have flow meters. When the pump goes on the little discs drop inside the vials

 

[swiflee]

what temperature is blending valve on manifold set to aswell?

Its on 5 (highest setting). But the same happens even if I remove it completely. I stripped both flow and return valves earlier and checked the pins were moving freely and there was no mechanical blockage.

 

[jonnyswamp]

Turn boiler stat up until u/floor flow pipe gives enough heat to manifold (try 70)
Is u/floor completly full of water without any air present and all valves on mani open (flows and returns)
Then find out why flow is loosing heat from boiler to mani (ceiling void open to elements or draughts, no lagging ?)
I assume new build, so maybe not fully finished