Water underfloor heating

Does anyone know anything about water underfloor heating?

The jist of the story is my parents bought a house with underfloor heating fitted and its never worked right. About 2 years ago they had a new boiler fitted, a new pump on the UFH, a new mixer valve and Nest fitted. The pump now works but the UFH is still faulty, another plumber took a look after the initial one was out of ideas and they didn’t have any real ideas. No plumber seems to wants to touch it as no one nows the pipe loop lengths so they cannot set the flow rates.

Before I go ahead and change the way the pump is plumbed in (I think the piping of the pump is causing the issue!) I thought I would ask on here.

It is piped in like this, flow from boiler at the bottom, return to boiler at the top, heat to UFH on top rail, return from UFH is the bottom rail.

My issue is that I don’t actually see what the pump is doing as surely the pump will just send the mixed water back to the boiler as that is the path of least resistance, rather than pumping it round the UFH loops.

Are the zone valves actuating to open the valves? If not you should be able to take the valve head off and push the pin down to see if that zone heats up.

IANAE but I thought the Flow should be go though a thermostatic mixer where the water temperature is lowered to 40deg by adding in cooler water from the Return.

I think you might be right, it has been assembled wrong possibly. can you see what make it is anywhere?

With ours there is a sort of mixer between the pump and the boiler. The mixer is controlled by the boiler and there is a separate thermostat on one of the pipes as it goes under the floor.  The idea is that the pump drives the water round the circuit and the mixer allows in enough hot water from the boiler to keep the pipes and a certain temp.   You need the mixer as the water temp for underfloor is a lot lower than the regular rad circuits and there is also quite a low maximum, something like 32degs

Edit: with ours it is also possible to manually move the mixer if you press an override button.  If the pump is running then you can move the mixer to see if you actually get warm water into the pipes

The mixer valve is just after the hot water stop tap in the picture, on the feed from the boiler. It is connected to the bypass pipe with the temperature gauge on it.

Its an old JG speedfit manifold.

I would try and download an installation manual for the boiler and check all the correct parts are wired up.  I would also check the connections to the boiler if the temp send unit isn’t wired up, for example,I would expect the boiler not to drive the pump at all.  You might even find the manual in the house

This is also my job over the Christmas break.  Ours has stopped working and the last time it was due to the underfloor controller having died. I suspect it has died again as in the programming u it the options for setting the time for the underfloor have gone

I think the pump and mixer are the wrong way round, mixed water should go into the flow manifold, return water from manifold is mixed with flow water to keep temperature down

Here’s mine (self installed)
Works great.

You can see the flow & return on the left in 15mm speedfit. Flow going into the UFH on the red isolation valve, return on blue.

Is it working in any/no zones or some zones? The UFH manifold valves are like frequent consumables on our system.

Max flow temp is 45degC nowadays.
If you can run lower and get desired temperature fine.
Thermostatic Mixer valve (which I assume has a clicky head to change temp pointing down) looks to be the item after the red valve.
Possibly pump is on wrong way round?

Assume by not working properly that house isn’t getting hot?
Common issue is room thermostats are linked to incorrect actuator head so some rooms overheat and others are cold.
If you have no drawings see if you can work out which pipe goes where. In theory the pipes shouldn’t cross under the floor so you should be able to work out which room first.
Can electrically work out which stat goes to which head.
Label all the actuator heads. Say A-F and the pipes 1-6.
Take all the heads off.
Do all the rooms get hot.
Do the flow and returns get hot (may take some time for the return to get hot if no heat in floor.
Do the flow indicators do anything?

Is the heating flow coming in on the bottom left pipe. Red Valve?
Return top left Blue valve?

Setup in that respect is fine I just can’t find an image to confirm pump is in the correct orientation.

Do the actuator heads move on operation. Slow to bring up a centre ring on the top when thermostat opened.
3 zones we can see they are all shut.
Once actuator removed do the pins move up and down. Use flat of a screwdriver and press down on them.

So I popped up to see my parents earlier and have a quick look at the UFH manifold. The plumber had shut off almost all the valves. I have opened them up a bit and all zones are now receiving flow according to the flow meters. I will go back up tomorrow and try to get them receiving hot water, that might be the bigger challenge!.

So I think I have got to the bottom of the issues and it was pretty obvious now when I think about it but its not something I ever thought to check.

The “plumber” that has installed the new boiler has piped the flow and the return the wrong way round into the existing central heating system. The flow from the boiler is very hot and then the manifold for the upstairs radiators heats the wrong way round with flow passing through the actuator valve the wrong way and that gets hot a long time after the return is up to temperature. Obviously the heating upstairs is working fine this way as it’s not fighting against a pump trying to pump water in the wrong direction.

I have helped install an under floor system. We used a thermal image camera to help us see where the loops were, and how the heat was distributed post self levelling compound being lobbed on top. Was amazed by the clarity through the screed, you could see exactly where the pipe runs were and the heat given off.

The “plumber” that has installed the new boiler has piped the flow and the return the wrong way round into the existing central heating system.

Weird. AFAIK most boiler flow & returns are in the same location, looking at the front, flow on the left.
I wonder if the old boiler had been installed incorrectly?

Feel which 22mm pipe coming out of the boiler is hottest/heats up first. Should be the flow.

Yes the flow is on the left and the return is on the right. Where the old pipe work goes up into the loft space the plumber had labeled the flow as the return as it has a R on it.

I am just going to get some speedfit pipe and fixings and turn the 2 pipes round. That way if it doesn’t sort it (and I am pretty sure it will) I can return it to how it was with minimum hassle.

Flow and return changed round and we how have working underfloor heating, happy days!

@singletrackmind. When we bought our house we had the survey include IR imaging of the floors to make sure the UFH was working. Images were very clear of the loops