No flow through UFH?

[Cliff11]

Hi Guys,

see attached pics.
Can anyone help with the following issue;
I had UFH system installed last year for my kitchen extension, the system was working ok when the plumber finished but as it was completed in the summer months the system was left off until required during the winter months but when I tried to run it I found the following:-
1/ zone valve opens to feed the pump OK.
2/ pump starts and water starts to flow through both of the UFH coils as indicated on the manifold flow indicators.
3/ Thermostatic valve is set to mid position 45.
4/ Temperature on the manifold inlet coils start to warm up and the return coils start to cool as the cold water from UFH returns to the outlet manifold.
5/ after 2 or 3 minutes the flow indicators start to drop back indicating no flow?
6/ increased the Thermostatic valve to Max and the flow indicators start to show a flow again but quickly drops off to show no flow?
7/ when I check the return coils to the outlet manifold they are still quite cold.
8/ when I check the thermostatic valve return to the boiler it is very hot.

My first thoughts were to check for air in the system and I did find quite a bit of air which I dealt with by refilling and flushing through each coil but the no flow problem still exists.

I think I will now have to remove the thermostatic valve and check for any blockages.

Any thoughts or advice on this issue would be very welcome.

Thanks in advance, Cliff.

 

[Timmy D]

Hi,

Not trying to be pedantic, but it doesn’t look like you have thermostatic heads on the zone valves.

The following maybe wrong (please correct) but I assume what you are referring too when you mention thermostatic valve is the mixing valve below the pump.

The mixing valve does not control the temp of the zone/room, only the water feeding the zone. Typically you want around 45c for screed floors and around 55c for timber/floating.

Have you tried unscrewing/removing the red caps on the thermostatic valves? The caps screw down onto the valve in absence of the thermostatic head. You can manually control the flow (thus temp), by manually opening/closing the valve via the red caps.

If you remove the caps (not flow meters), you should get full flow.

You can also loosen/tighten the flow meters to increase/decrease flow (like a radiator lock shield valve to balance the zones, a larger zone requires more flow).

I find it odd that each zone doesn’t have a thermostatic head/actuator which is connected to a wall thermostat located in the same room as the zone. This allows the system to manage the zone/room temp dictated by the room stat.

Do both zones feed the extension? Do you have a stat on the wall? One stat can feed multiple loops.

Was this of any help?

On the attached picture, pretty much the same set up as yours, you can see the thermostatic heads I mention.

 

[Brambles]

Yep, you don’t appear to have any actuators. Get the installer back asap

 

[Ben-gee]

It maybe just one room.

I have this set up at home in a large kitchen/diner extension; it has two loops like the OP. I have no actuators as the room stat is linked to the zone valve and pump on the ufh and this controls it nicely - the two loops are to get a more even heat but they act as one effectively.

 

[Cliff11]

Thanks for the reply’s guys, FYI you are correct I don’t have thermostatic valves as the room stat is linked to the zone valve and pump on the UFH which controls the room temperature.

when I mention thermostatic valve I meant the mixing valve under the pump.

I have checked the red capped valves and they are both fully open.

Yes both zones only feed the extension.

When I was flushing the air out of the UFH one zone at a time I could see a good flow through each flow indicator so I know both zones have been bled OK but when I restart the system I find I still have the same problem when the pump starts the flow indicators show a good flow for a minute or two then the flow drops off to zero?
I think the mixing valve may be blocking up?
Or the pump is not fit to push the water back into system?

has anyone experienced this issue before?

 

[John.g]

Can you check what mode the pump is set to (also which Grundfos model) it may display the head pressure and the actual flow rate, it will certainly show you what mode its on and the power in watts, this info should be useful for trouble shooting.

 

[Cliff11]

thanks for the reply John, see attached pic with pump details, the pump is set on the third speed.

 

[John.g]

Also is the boiler temperature higher than the required UFH temperature, if not then the thermostatic valve may just recirculate all the water straight back to the boiler after a few minutes.
[automerge]1602319519[/automerge]

thanks for the reply John, see attached pic with pump details, the pump is set on the third speed.

Thanks Cliff, ignore my post #10 above as I got a bit mixed up, the lower the boiler temperature is, the less water the UFH pump has to re circulate, if the boiler temp and the thermostatic valve settings are the same then there should be no recirculation and all the water is returned to the boiler after passing through the UFH pipework.
Can you hear the pump is actually running?, if not sure remove the vent screw and you might be able to see the shaft turning, if not, you should be able to free it up by using a screwdriver in the slotted end.
If pump running, change speed setting to speed1 as speed3 is over 6m and the boiler circ pump may not be able to supply sufficient water to feed it but you should hear the UFH pump noisy/cavitating. Also make sure the pump setting is on the constant curve mode, I think the LEDs to the left will be illuminated and if on PP mode the LEDs to the right will be illuminated.
That's all I can suggest re any pump problem(s) but obviously could be a blockage/stuck thermostatic valve or some other reason.

 

[Cliff11]

Thanks for the suggestions John. I just checked the pump by removing the vent screw and I can see the internal screw head isn’t turning, tried to free off the pump impeller but I can’t get it to turn so I guess it’s seized up which is a bit strange for a new pump that’s never really did much work? The screw head on the impeller is a strange star shaped drive and I’m struggling to get a screw driver to fit correctly so I cant put much force on it, anyone know what type of driver I need to free off the Grundfos pump as seen in my earlier post?

I guess the short flow that I can see through the UFH when I start running the system is just the CH system pressure flowing into the zones.

 

[John.g]

Your post only appeared a hour ago, when you have 10 posted it appears straight away.

I am not familiar with the Grundfos range but if you are careful not to damage the electronic "bit" you may be able to remove the head complete by removing the 4 securing stud bolts, you should then be able to view the impeller (maybe you have already done this?) and pump ports for any debris and clear it out (assume you can isolate the pump without system drain down), OR the pump may be under warranty and you may be able to get a replacement but your plumber may have to do this if he supplied it, don't know how strict they are with replacements if it is found that it is full of crap. I presume the system was flushed out properly on installation, so might be best to get your plumber back and see what he says.

 

[Cliff11]

Your post only appeared a hour ago, when you have 10 posted it appears straight away.

I am not familiar with the Grundfos range but if you are careful not to damage the electronic "bit" you may be able to remove the head complete by removing the 4 securing stud bolts, you should then be able to view the impeller (maybe you have already done this?) and pump ports for any debris and clear it out (assume you can isolate the pump without system drain down), OR the pump may be under warranty and you may be able to get a replacement but your plumber may have to do this if he supplied it, don't know how strict they are with replacements if it is found
that it is full of crap. I presume the system was flushed out properly on installation, so might be best to get your plumber back and see what he says.

Thanks for the reply John, Ill get my plumber back as the system will need to be drained and refilled to allow us to check and replace the pump if required.
I’ll let you know what we find once we get the pump opened up👍