Underfloor Heating system wrong flow direction?

[camobrie]

Hi,

I’ve inherited this ufh system and having trouble after trouble with it. Had someone out 3 times but still problematic.

Flow from gas boiler bottom left, return to boiler top left.

Current issue is return pipes are roasting hot and supply is cold/lukewarm. Flow meters all read 0 and are filling with air bubbles.

Settings are:
Thermometer bottom left - 70
Pump - 3
Mixing valve(red box) - 55

The floor for the 1st zone does heat, 2nd and third zone do not. Actuators open correctly when zones call for heat.

No matter which way turning any flow meters, doesn’t raise or lower the flow rate.

Any ideas? Thanks!

 

[Roddy Young]

Hello,
Our UFH is identical, also labelled Rehau. The boiler feed is to the bottom via the thermostatic valve as yours.
The thermostatic head (bottom left) should be set to about 30 or 35 degrees. It has a capiliary tube going to a capsule at the right end of the lower Manifold feeder.

One thing: the flow rate is not adjusted on the flow meters. There is a square spindle under each actuator.
See attached Rehau info book page 8

It sounds like your pump is not working and any warmth in the return UFH pipes is conduction from the lower feeder.

 

[camobrie]

Hey! Thanks for the help. I removed the caps and fully tightened the control spindles to cut off flow completely(picture1) (unsure why the left one stopped much higher than the others?)

Then as in manually two turns anti-clockwise(pic 2) however did not see any change in flow meters. I also made sure that flow meters are open by fully turning anti-clockwise as on page 10.

Any ideas how to test pump? Had a plumber out who took it out of the system and tested independently which all looked ok.

Edit: also the themostatic head has a range of 40 -> 70, unsure how to solve that for getting to 30-35

Cheers!

Pic2:

Pic1:

 

[Roddy Young]

You have had the pump itself checked, so if it's not working you will need to get a meter and check its supply. The red box should do the switching but it, in turn, needs a supply. Maybe that's not being provided by the controllers. Our controller is a long box with leds which light to indicate which circuit should be on. It also switches on the pump. If the pump relay has failed in your controller, you won't have a feed to the pump.
You could test the actual plumbing by wiring the pump to a 13A plug and see if the pipes warm up correctly.
Your boiler probably has a pump which is feeding the hot to the lower manifold pipe. That probably pushes the hot water backwards around the system at present.
If the pump is working OK, then you could also look at the mixer arrangement at top right under the red box. I've never been in ours so can't tell you much about it.
The thermostatic valve should be OK at 40 degrees. Ours is set lower so the floor temperature cannot exceed 27 degrees - prescribed by the flooring manufacturer.
Roddy

 

[cathalsmurf]

Hi Guys,
I've a similar system here and have been having issues over the past few days. Turns out there was an electrical issue with the pump and is now working again and starting to warm up incredibly slowly. As I was looking at it I couldn't understand why the feed from the boiler is connected to the 'return' rail on the manifold, then goes through a pump and only then to the 'supply' rail. This would appear to be backwards. Does anyone know why it runs this way?
Thanks
Cathal

 

[Roddy Young]

It does seem counterintuitive but I guess someone at Rehau discovered it was good to circulate the water around the floors with their pump (imagine both boiler connections shut off....) and top up the temperature as needed by the bleed of hot water through the thermostatic valve bottom left. Maybe this gives a more even temperature through the whole floor circuit.

 

[dilalio]

If pump is good and all pins and flow meters can be confirmed open then I would look for blocked UFH loops.

 

[dilalio]

It does seem counterintuitive but I guess someone at Rehau discovered it was good to circulate the water around the floors with their pump (imagine both boiler connections shut off....) and top up the temperature as needed by the bleed of hot water through the thermostatic valve bottom left. Maybe this gives a more even temperature through the whole floor circuit.

This is how hydraulic separation is achieved, so that the lower flow temps of UFH can be separated from the higher flow temps of Radiators and cylinders.

In an installation which is all UFH, boiler flow temp can be set to low for UFH and no mixing is required.

Hot water can then be handled using PDHW and dual power mode within the boiler.