Radiators and UFH not functioning well

Hi All.

First post.
What a great bunch of people here.

I have recently had an extension done and we have UFH on just the new extension, and radiators upstairs etc, in the house we have a nest thermostat and a heatmiser stat for the UFH area. The issue I am having right now is that the nest is the only control for heating the radiators and UFH, the UFH thermostat doesnt seem to have any effect. UFH takes some time to warm up, and when the radiators are very hot upstairs, the UFH is barely warm, so ideally I want the UFH to be able to demand heat independently from the radiators.

There are 2 x 2 zone port valves, and 2 pumps, 1 for UFH and I dont know what the other one is for. The UFH is a 2 zone system but connected as one due to the size of the area. The manifold has 4 ports.

The boiler is a 30KW system boiler.

Can someone please explain what is missing/wrong here and what needs to be done to remediate it.

Thanks in advance.

Should be 3 two port valves. One for radiators, one for under floor and one for hot water cylinder.

Was it a plumber who installed or a builder?

SimonG said:

Should be 3 two port valves. One for radiators, one for under floor and one for hot water cylinder.

Was it a plumber who installed or a builder?

Click to expand...

As you rightly mentioned, there are 3 nos of 2 port zone valves.

I can see one attached to the cylinder, I can see another 2. I think the issue is to do with the wiring and control, what should go to where/contral what.

Is there a sketch or wiring diagram that I can use to crosscheck what has been implemented, I believe the builder subcontracted to a plumber.

Thanks in advanve.

The UFH should be on its own zone, as should any other load circuits. Can you confirm the radiators are off the same zone as UFH?

The ufh will take a while to get upto temp 12 hours normally depending on the system

S plan plus is the system you have

Shouldn't run the underfloor as an on /off system, except off in summer. It should be more of a temperature based control to give a higher temp for occupied periods and then lower, set back temps, for periods of occupation, i.e. overnight.

Have a look at the Honeywell website for a wiring diagram of an s plan plus system.

Definitely sounds like it's not wired correctly.

ShaunCorbs said:

The ufh will take a while to get upto temp 12 hours normally depending on the system

S plan plus is the system you have

Click to expand...

Thanks for the reply, I have done a sketch below of how hot water flows in the system, what I cannot do is open up the electrical connections as I wouldnt understand this, the key thing that I had like to understand is that how should this have been wired to achive the goal of the 2 thermostats being able to call for heat independently?

Nest = Rads
Heatmiser = UFH

The nest controls everything right now, the zone valve before the manifold doesnt appear to be doing anything.

Op - your best course of action is to get the builder / plumber / sparky back

This issue is so so common ....

If the system was designed and installed by a plumber, my advice would be to get him back to commission the system and explain its control philosophy and operation to you.

Failing that you really need to post a schematic diagram of the full system (including main pipe diameters) to get meaningful feedback.

In my experience it is more likely to be a design or balancing / commissioning issue rather than a simple control reconfiguration.

Adding and effectively controlling an UFH to an existing panel radiator system is not as straightforward as it often appears.

You say that the Nest is controlling both the panel radiators and the underfloor heating (unless you have two Nest thermostats) they ( the UFH and radiators) are being treated as one zone. I don’t think that is the case. If it were, you would not have a Heatmiser control incorporated into the system. If however the Heatmiser is configured as a sub zone to the main panel radiator heating zone, then it will never work effectively.

If you are unsure, set the Nest to its lowest setting for a few days and set the Heatmiser to at least 25 degrees ( because it is warm outside at the moment). After 48 hours the rooms with UFH should be up to temperature, have warm floors, but all the panel rads should have remained cold.

The UFH requires separate zone control to the panel radiators, the mixing valve properly set and ideally a separate return direct to the boiler or low loss header.

Hope this helps to give you sone direction as to the areas to look at.