Underfloor heating not warm on all circuits

[gus_uk]

I have 6 circuits of underfloor heating on one manifold. The first 4 circuits are through a concrete slab the last 2 are under a suspended floor.

The first 4 are great, they warm up very quickly, the last 2 do not heat up much at all. In trying to diagnose the problem I have turned off the first 4 circuits at the actuator valves and left the last two circuits on, initially together and subsequently separately. After many hours the floor is barely noticeably warm.

I tried bleeding the system, only water came out.

Currently the system is controlled by one thermostat which turns everything on at the same time. I do intend to upgrade in future to control actuators to individual thermostats.

It doesn't make any sense that the circuits under the suspended floor are so radically different from the other circuits, I have been told that it has been fitted with trays and insulation correctly.

What other causes could there be? or tests I could do on the system?

 

[BigSnoopy01]

Are you saying the rooms are not warm or the floor temperature or both? The concrete acts as a heated mass so but the timber floor won't give the same feeling.

 

[trojanhawrs]

What type of flooring do you have over each of the loops?

 

[gus_uk]

Many thanks for the responses

tiled floor which is the same across all the underfloor heated area

in the 2 circuits both the floor and the room are not warm

when closing the first 4 circuits and leaving only the last 2 circuits for the timber floor the heat is only just detectable when putting a hand on the floor.

 

[trojanhawrs]

Can you open up the flow any at the manifold ?

 

[Madrab]

Are the loops out to the suspended floor hot on the flow and cool on the return?

 

[gus_uk]

I have opened the flow at the manifold as much as possible

The loops on return are cooler, I have been measuring the return and adjusting the flow to try and get it close to 7 degrees difference on all loops. The last two loops (covering the timber floor) have a difference of less than 10 degrees, when all the loops are on then the last loop has the lowest temperature going out, about 10 degrees lower than the hottest loop. I am considering investing in auto balancing actuator valves which will sort out some issues but I can't see it impacting the low floor temperature of the timber floor.

 

[Madrab]

Ok, I think there has to be an understanding that the 2 different floor types will not react in the same way. The wooden suspended floor needs to be controlled separately and more heat fed to it as wood will act as a thermal insulator whereas concrete acts as a thermal conductor. That being the case the concrete slab will always react faster and feel warmer that the wooden floor.

Unfortunately the big mistake was the installer didn't know what they were doing setting it up on the same system. The problem is when retrofitting the suspended floor that the wood was retained, do you know if any PIR insulation etc was installed below the suspended floor or is it just the spreader plates? The best way to retrofit UFH into a suspended floor is sheet underneath, fill with PIR, lay the UFH pipework onto that and then top it with a biscuit screed, or then use the spreader plates, then a cementitious flooring goes on top of that.

You are now in a position whereby you are trying to balance the heat output in an UFH system when it is using 2 different types of flooring that performs completely different. If you keep them running on the same system you may find that it will be nigh on impossible to level them out. So it may be time to rethink.

 

[gus_uk]

Thats really helpful, thank you - I will see if I can contact the installer and check exactly what the setup is.

Do you think it would work to setup the two different floor types with two thermostats controlling the actuator valves for the different floor types.
i.e. Thermostat 1 controlling valves 1-4 concrete floor and Thermostat 2 controlling valves 5-6 for timber floor?

 

[Madrab]

To try and understand what you have, is it - 1x2port valve on flow > 22mm flow into a thermo blending valve > through into the pump and then into the manifold then 22mm return back to the main system? You say you have 1 stat controlling the whole manifold, so is that connected into a control centre or does that control the 2 port, if there is one?

The way I would look to approach it would be s - when looking to doing this, shut down the UFH in the loops that run through the screed, then try and bring the suspended flooring up to temp, that will tell you if the system can actually cope with that part of the UFH. If that succeeds then you can try and balance the screeded section.

You say you are getting in touch with the installer, when was this system put in and has the suspended area ever been warm enough?

 

[gus_uk]

Picture attached - although not a great angle and pipes in front of the manifold which are not part of the heating. Yes it is as you described.

1 stat controlling 2 port valve. No control centre (yet!)

The system was put in 2 years ago. I don't believe the suspended area has been warm enough which I thought because it wasn't balanced. The installer didn't measure the lengths that were put in so it isn't possible to make the calculations to balance.

I will try as you suggest and shut down the loops through the screed and see if the suspended floor gets up to temperature. Thanks for the advice.

 

[Madrab]

The system wouldn't really be 'balanced' as such, each loop should have it's flow set to Kw output per M2 as per its pipe centres/temps etc. That and the input flow temp set correctly at the blending valve but that should all have been designed and set up correctly by the installer to ensure it meets it's designed outputs.

If none of that was done then I have to say that they haven't really done their job properly. Was there any CAD design paperwork created showing the layout and outputs etc?

 

[gus_uk]

I tested the different loops last week and the two under the timber floor do heat up eventually.

Unfortunately there are no CAD drawings, very frustrating that a proper job was not done.

What would be the best approach to improve this? Seperate thermostat controlling the actuators for the different types of loops?

 

[Madrab]

What would be the best approach to improve this? Seperate thermostat controlling the actuators for the different types of loops?

All that will do really is allow each loop to be independently controlled, i.e. it's own zone.

If it was me then I'd be shutting down the screeded sections and concentrate on the suspended floor and see if the flow and temp can be set so that it gets up to temp at a reasonable rate, that will show whether the spreader plates under wood setup is actually capable of doing what you want it to do. If it isn't then there may not be much you can do with it with the current setup.