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

 

[swiflee]

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

Tried turning the stat up. Makes no difference apart from the Rad circuit getting toasty :vanish:

All mani valves are open / off and there is no obvious signs of air... but the issue is the manifold flow bar cooling down. I cant fathom this part out.

Its a refurb, changing from vented to unvented with new pipework so all ceilings are down.

 

[dancinplumba]

Shut the rads off

 

[jonnyswamp]

Restriction or air in flow (or return)to mani from boiler, as said above shut rad circuit 2 port and try
If that don't work, I would disconnect flow and returns from primaries and mani and try hosing through both

 

[walterwhite]

Start again. Finish wiring it & commission it properly. Put valves on to auto. Get a plumber in is the best advice

 

[swiflee]

Thanks guys. Next step is to isolate the UFH circuit as you've said and try.

Will post the update here.

Have also got the tech guys from the manifold supplier (well known) on the case.

 

[walterwhite]

You haven't finished installing it yet! I bet it hasn't been balanced either. Flow rates for each loop need to be set. You will get heat going through to the ufh when you have manually opened the 2 port. Am I missing something or is this a wind up?

 

[dancinplumba]

Can you put a PIC up of manifold

 

[swiflee]

Here you go. Just to confirm that the white nuts on the bottom rail are all open. I just fixed them in place so I didnt lose them.

And I closed all the flow meters down except the last loop nearest the bypass valve just to see if we could get the heat across the manifold when the pump was running.

 

[walterwhite]

I've never seen a manifold plumbed like that.

 

[jonnyswamp]

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

So if the flow meters indicate you have water movement through u/floor, problem with restriction in dedicated flow/return
Your central heating pump should supply hot water to the manifold, then the pump on the mani does the rest
If your mani pump is moving the u/floor water around then its a supply problem I would have thought
Not seeing first hand so guessing really

 

[dancinplumba]

I've never seen a manifold plumbed like that.

me either

 

[dancinplumba]

whats the copper pipe on rhs of bottom manifold ?

 

[Chalked]

whats the copper pipe on rhs of bottom manifold ?

It's the return to boiler. The chrome pipe above is a bypass.
It's a Wundafloor system by the looks of it.
The problem is very simple. Your motorised vslve is being held open manually.then your main pump can force water throght the loops.
Job need finishing,wiring up and testing. If you let the motorised vslve close msnuslly it will stop getting warm.

 

[Matt06]

thats return by the looks

and i guess there is non return in the bottom right end of manifold to prevent pump drawing from the return

 

[magicno1]

thats return by the looks

and i guess there is non return in the bottom right end of manifold to prevent pump drawing from the return

It don't look like there is
Weird set up this one!

 

[tolly]

me neither, cant see the need for that chrome bypass pipe either.

 

[Chalked]

thats return by the looks

and i guess there is non return in the bottom right end of manifold to prevent pump drawing from the return

On these, the non return is on the left hand side of the manifold. Just before the pump. The bypass works when the pump starts up an before the heads have opened.

 

[walterwhite]

I don't like it., but chalked has answered the OPs question in #23

 

[swiflee]

Thank you Chalked. Yes it is a wundafloor and everything you have said about the bypass and boiler return and non return is correct.

I thought I would have been able to at least get hot water circulating through the manifold (even with the loops closed) at the boiler temperature with the motorized valve on manual and certainly no flow temperature drop when the circulating pump is switched on irrespective of whether any controls are wired.

There is a pump in built to the boiler as its a system one.

 

[Gray0689]

It's the return to boiler. The chrome pipe above is a bypass.
It's a Wundafloor system by the looks of it.
The problem is very simple. Your motorised vslve is being held open manually.then your main pump can force water throght the loops.
Job need finishing,wiring up and testing. If you let the motorised vslve close msnuslly it will stop getting warm.

Exactly what he said
Get it wired correctly and jobs good