I Need Your Help! Underfloor Heating Not Working - Flat with HIU

[UFH_MONO]

Hi Plumbersforums Experts,

I have a question that I hope the experts in this forum can help me with.

Our underfloor heating (water) has stopped working a few weeks ago. We live in a new-build block of flats with a central boiler and an HIU unit in our flat.

I have asked two engineers to come to check and they have had different recommendations.

The first one spent 5 minutes looking at the HIU unit and said the pump needs to be replaced (Grundfos UPM3 Auto L pump, with red and orange light on). Because this engineer didn't seem very trustworthy, I asked another one to check.

The second engineer said yes, the pump needs to be replaced but at the same time, we need a power flush because we have no pressure at all. He was confident that only replacing the pump would not be sufficient.

Obviously, the power flush will be very expensive. I wanted to make sure it is needed before we spent a vast amount of money.

How do I know whether it's just about replacing the Grundfos HIU pump or whether the power flush is actually needed?

A few facts

• We still have hot water throughout our flat.
• The HIU makes some weird clicking noises, like a clock.
• Upstairs (we have a duplex apartment) I hear that the pump tries to get going, makes some noises every few seconds but fails to gear up.
• No heating in the flat.
• The pressure indicators indicates 0 throughout.

I am attaching a few pictures.

I really hope some experts here can help or tell me what to look out for and how to go forward.

Thank you so much!

Lisa

 

[UFH_MONO]

Those are the notes from the engineer.

• Work description: heating not working from the HIU.
• Identified that both underfloor heating manifolds have 0 pressure
• Checked both underfloor pumps are working I have turned the thermostats off so that the pumps do not burn them selfs out.
• The HIU unit needs full service. It also has 0 bar of pressure.
• The pump on the HIU is faulty it has burned its self out where the system has no pressure. The same pump needs to be ordered to fit in side the unit.
• The actuators on the underfloor are all working correctly
• The customer has hot water but the heating is off until more works are carried out.

 

[Timmy D]

Need to know what HIU you have. I’ve not worked on these units but just had a read on google to get familiar.

My understanding is as follows (some of what you’ve wrote/been told doesn’t make full sense).

Hot flow/return come from the building and heat your hiu. This is working as evident from the hot water.

Most units will have two separate phe’s (plate heat exchangers), one for heating, one for hot water. The phe’s keep the building water separate from your apartments water.

The buildings water can have pressure in one side of your phe’s (primary), and your side (secondary) of the phe’s, none.

The hot water side of the hiu, can be pumped/unpumped. It seems the standard option is unpumped.

Heating phe will always be pumped (this is the pump which is dead.

As this pump is dead, it can’t move the heat from the heating phe to your underfloor heating manifolds.

Pumps can be electrically tested to confirm if dead. I assume it has, so this is a certain required replacement.


The second issue is no pressure.
As the secondary side of the heating phe is completely seperate from the primary, there must be a filling loop on your system to allow you to top up the pressure.

You need to find this filling loop (potentially 2 valves connected with a braided hose or it could be internal of the hiu. Once found the pressure should be topped up to around 1 bar.

You will then likely need to bleed some air out of the system.

If you post more pics (hiu/all pipe work etc)/hiu Male/model, we should hopefully be able to locate the filling loop.

I can’t see why you’d need a flush on a new build underfloor heating system (it’s new/sealed/no rads to corrode/produce sludge/a blockage).

I would get a new pump fitted, get the pressure back up and expect all to be well.

Forget about a flush until proven (highly unlikely).

 

[UFH_MONO]

@Timmy D Thank you so much for your detailed reply! It's incredibly useful.

I also thought the power flush just didn't sound right. Your troubleshooting sounds like a very likely solution. I will look further into it.

Thanks again for taking the time to read through my initial message and taking the time to reply, have a wonderful evening and weekend!

 

[ShaunCorbs]

Would say your problems are down to no flow / no water in the system need to top the pressure upto 1 bar then air the system and try again

 

[king of pipes]

I would tend to agree with the chaps above these units need servicing the system is low on water and it may well be that a pump is goosed ? , but these particular pumps have a built in protection to avoid burn out they can get stuck as the impeller is quite small if on a dirty system or left isolated , I had to free off one on a underfloor system this week isolating the supplies removing the pump to see if it's runs free would be my advice first .The system would probably benefit from a flush through but not necessarily a full power flush I have often used the internal cold water mains supply to flush the unit and system through this removes any debris in there and add fresh inhibitor as I said before these unit need servicing and often they are fitted and forgotten about. Kop

 

[UFH_MONO]

An update on what happened: The HIU pump was replaced, pressure reintroduced and the system is now working!

However, I have another problem now: Downstairs, the thermostats keep tripping.

When I switch on the heating, the thermostat downstairs is fine, but then after about 5 minutes, they go completely off (looks like no more electricity in them). They do turn themselves on again if I switch the heating on / off, but again, after 5 minutes, they go.

Upstairs, everything seems fine.

Does that sound like a wiring problem? Any ideas?

 

[ShaunCorbs]

Are they battery units or mains powered ?

 

[UFH_MONO]

We have the Emmetti thermostats (see picture, this is a thermostat from upstairs) that are mounted to the wall. I believe they are mains powered.
The thermostats downstairs are all completely blank after a few minutes of turning the heating on (not even on off, but blank).

 

[Timmy D]

We have the Emmetti thermostats (see picture, this is a thermostat from upstairs) that are mounted to the wall. I believe they are mains powered.
The thermostats downstairs are all completely blank after a few minutes of turning the heating on (not even on off, but blank).

View attachment 46749

Isn’t that odd. Really you’re gonna need a multi meter, and an understanding of how to test.