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[Darryl Smith]

Hi, I recently bought a cottage which has underfloor heating supplied by a combi boiler. It doesn't work. There are two zones as can be seen in the photo and I am going to attempt to flush the system which seems pretty straightforward. The problem that I have is that there's no isolation valve on the return (lower) return manifold. I'm not sure how to isolate the system and was hoping someone could have a look at the photo and give me some advice. Thanks in advance. 

[ProDave]

Before you try that (which may not be necessary) you first need to find out exactly what is not working.

 

So with heating on and all room thermostats turned up, is the pump in your picture running?  Do ANY of the pipes on the manifold feel warm, especially the copper ones?

 

If they do, but the white pipes are not warm, try unscrewing the two actuators on the bottom, With them removed the zones will be on regardless of thermostats.

 

And do remember UFH is not instant like a radiator, it can take a long time to warm up.

[Alan Ambrose]

Yeah, agree with that.

[Darryl Smith]

On 01/11/2024 at 12:57, ProDave said:

Before you try that (which may not be necessary) you first need to find out exactly what is not working.

 

So with heating on and all room thermostats turned up, is the pump in your picture running?  Do ANY of the pipes on the manifold feel warm, especially the copper ones?

 

If they do, but the white pipes are not warm, try unscrewing the two actuators on the bottom, With them removed the zones will be on regardless of thermostats.

 

And do remember UFH is not instant like a radiator, it can take a long time to warm up.

Hi Dave, I've done everything you've suggested and heat gets to the manifold and into the beginning of the infeed. The outfeed pipes aren't warm but that can be expected due to heat transfer. However, the floor doesn't get warm even leaving everything on for days. As an engineer I understand how the system works but don't understand how to isolate the return manifold. This is partly due to the fact that it's very difficult to trace where the pipes go in a 400 year old cottage. 

The circuitust have been filled initially so I'm assuming that the return manifold can be closed off. I've tried shutting off the Magnaclean unit and hooking up a hose, etc but when I shut off the supply from the hose, which should mean no water flow in the system, there's still water coming out of the return manifold. I can only assume that it's back flowing or syphoning from somewhere else.

[ProDave]

Sadly it has been plumbed wrongly.

 

There is a perfectly good isolating valve on the bottom manifold, completely un used.  The bottom connection to the manifold should have been connected there, and I am certain that unused isolator could be swapped to the left hand end where it would then work.  But you would need a plumber to do that, unless you are good at DIY plumbing, which would mean draining down a large part of the system just to move that isolator somewhere useful.   

 

Once done you would be able to isolate the top and bottom manifold and flush the UFH pipes through with water.

 

Are there any flow meters on the top manifold hiding out of sight behind the pump?

[JohnMo]

Are the isolation valves either side of the pump open?

 

With pump on, do you see flow on the flow meters - behind pump.

 

Your mixer valve - altering that, does it change anything?

[Nickfromwales]

Could also do with an automatic bypass between the flow before the mixing valve and the boiler return to deal with when the boiler is only (or very partially) servicing the UFH; where it then can’t dissipate the flow energy that the pump creates. Depending on boiler model it may have a modulating pump, if so not so much of an issue, but best to check so the boiler doesn’t self-destruct over time. 

[Darryl Smith]

7 hours ago, ProDave said:

Sadly it has been plumbed wrongly.

 

There is a perfectly good isolating valve on the bottom manifold, completely un used.  The bottom connection to the manifold should have been connected there, and I am certain that unused isolator could be swapped to the left hand end where it would then work.  But you would need a plumber to do that, unless you are good at DIY plumbing, which would mean draining down a large part of the system just to move that isolator somewhere useful.   

 

Once done you would be able to isolate the top and bottom manifold and flush the UFH pipes through with water.

 

Are there any flow meters on the top manifold hiding out of sight behind the pump?

Yeah, I couldn't understand why the isolation valve was on the wrong end of the manifold either. 

Yes there are flow meters which show that there's flow, red indicator at the top.

[ProDave]

1 minute ago, Darryl Smith said:

Yeah, I couldn't understand why the isolation valve was on the wrong end of the manifold either. 

Yes there are flow meters which show that there's flow, red indicator at the top.

Can you read the scale on the flow meters if so what is the flow rate?

 

That begs the question if the water is warm, and it is flowing through the UFH loops but never getting warm, then just what is the under floor make up?  and has it EVER worked properly?