underfloor heating problems

have just checked your link - looks like the valve i have, unfortunately my german/danish is that good anymore, and it makes no sense. ha. cheers.

have disconnected mixing valve head and moved the pin, you can heat it restrict the flow.

have disconnected half the actuator heads - pins move freely.

one thing that did happen. - fired up the ufh, the flow manifold got hot. boiler cut out on its on temp stat. then i isolated the flow port to the manifold, kept the return port open - and partially drained the system via the drain off on the ufh manifold. the return manifold heated up - which it would beacause heat flowing back from the mixing valve. now the ufh seamed to work for 10minutes ish, when i re-opened the flow isolator - only 2 loops were open. when i then decided to open the other loops, the return manifold went cold and nothing again. again made me think, mixing valve not working properly - seamed it needed to heat up first, which is why i thought the original design was plumbed in wrong (didnt know about the mixing valve being in a diverting position then)

apart from re-jigging the pipe work, i'm a little bit stuck on this one :)
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ah - i see. from what i understand - it mentions about the mixing valve being reversed. therefore my manifold could be the wrong way around for this mixing valve to work- but if my mainfold only works this way - then some pipework needs changing. hmmmm??
Its a diverting valve not a mixing valve. (If your valve is the one in the link)

The reference to reverse control refers to the electro thermal actuaters. Which is either on or off.

The thermostatic control actuater provides steady control or proportional control as they call it.
So the valve stem can move through a proportion of its travel and stop to provide the correct percentage of flow through the relevant ports.

You seem obsessed with modifying pipe work for some reason.
Have you seen the circulator impellar revolving when energised?
Have you tried running the system with the oventrop thermostatic head removed? (keep the boiler stat well turned down if you do this!)
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yes - the pump is definately working. i have only ever installed one other ufh heating system - uponor, where the manifold came complete with pump and relevant connections - so, my knowledge on this subject is very poor. The reason i believe for changing the pipe work is to incorporate a mixing valve and not a diverting valve - from what i understand it should be the premix entering the ufh flow.

as far as the customer is concerned (not my customer, but a friends) they just want it working, and i can only see that changing the pipework to incorporate a mixing valve into it, to do this.

the pump is a grundfos 15-50, have tried it on all 3 speed settings. have also tried disconnecting it and running ufh from central heating pump -with all rads closed to see if that worked. nothing.

dont suppose your local to dorking, ha.
Obviously I am too late for this guy but if anyone else has a similar problem no one mentioned to him that the return loops are fitted with non return valves. The clue is where he says that the flow indicators are sited on the different manifold from the original, so he was probably trying to pump the water the wrong way round. Another point is that no one picked up on his comment (in answer to "are the flow meters working?) that "I think so as the flow meters filled with water ....). The level of water in the flow meters is irrelevant (as long as there is some). If a flow meter is open and the pump is running (and the return valve open) then the indicator float WILL move down, irrespective of the amount of water in it. The indicator does NOT float on the water. When most systems are first commissioned the flow meter will fill to 60% or so, because air is trapped at the top of each meter glass. As the system runs, the water in the glass will be slowly replaced (there is no direct flow through the glass as the flow is sensed below the glass and in the manifold) through agitation and the air saturated water renewed, allowing more air to be absorbed and, therefore, more water to enter the glass.

The presence of the non return valves mentioned above, can also cause problems when initially filling the system if you, for convenient access purposes, try to fill it through the bottom (return) manifold.

Hope this helps someone.

An old thread i know but it may hold some relevance to a problem i,m trying to sort for a friend.

I installed my own NU-HEAT UFH system a couple of years ago and have had no issues at all. My friend just had the same system installed by a "profesional" and is experiencing eratic behaviour, ie some loops are not heating!

The first thing i noticed was the colour of the flow meters, mine are totally clear like fresh water his are a dark rusty red colour!! I flushed out each of his loops individually removing a hell of a lot of dirt although the meters still look filthy!

Is it possible for the flow meter to become clogged up with **** and then to restrict the flow to a particular loop?

How exactly do the flow meters work? Obviously they are adjustable to adjust the flow but what is inside, is it a needle type valve affair?

Can they be removed for cleaning?

As always thanks in advance for any help.


Most of what you want is covered in my post immediately previous to yours.

Do the flow meters indicate the required flow in any loop?

Effectively a flowmeter runs in parrellel with the loop not in series so it should be impossible for a blockage in the actual flowmeter to restrict the passage of water through the loop. The flowmeter receives a small amount of the flow, the pressure of which raises the flowmeter float. It is possible for one of the valves on the flow and the return of the loop to have been blocked.

Assuming the system has been properly installed (apart from the obvious omission to flush it originally!) each loop is NOT entirely independent. Each loop draws its suppl;y through an individual valve from the common feed (i.e. the supply manifold) and returns through an individual valve to the common return (i.e. the return manifold), so you can isolate each individual loop by closing both it's flow and return valves. Once this is done, you should be able to unscrew the glass viewing phial for cleaning.

You can, of course, close down the flow and return valves to the entire manifold and, being careful to allow the pressure to be released, remove them all at once. This is what you will have to do if you suspect there is a blockage in the manifold. If you do this, remember to remove and clean the automatic air release valve which will most likely also have become contaminated.

After flushing out (hopefully using a proprietary flushing additive and not just plain water) did you refill using a bacterial inhibitor? Otherwise you will find the loop contents will become green with algae - visible through the flowmeter glass.

I hoe you realise that the return valves of each loop are effectively one way valves so you must always flush through in the correct direction.

When carrying out the above, remember to isolate each manifold set if there are more than one (as is normal on houses with 2 or more floors).

Hopefully your friend now has a filter fitted - I prefer the Fernox TF1 which is both magnetic and centrifugal and allows easy top up with inhibitors when necessary.

All the best.
Taxes, first of all thanks for your concise reply, it is much apprecaited.

Out of 8 loops down stairs all apart from two were heating. Following my flushing a different two did not heat leading me to believe we have a variable in the system which can only be junk.

Yes the flow meters are indicating on the good loops although some seem to stay down when the actuator is closed!

Isolating individual loops --- I understand how to close of the return, remove the actuator and repalce it with the supplied screw on cap, screwing it down completely. However i,m not sure about the supply, does screwing the flow meter all the way down actually close it completely??

The complete heating system in this house is 100% brand new, for all intense and purposes this is a new build. How can their be so much **** in the UFH system?
Is it common practice to install a filter on a new installation these days? This system does not have one!!!

Ok i may get a chance to continue today, and will report back.

I can then move onto some questions about his hot water!! youve propably gathered by now the plumber is not in favour and is now out of the equation.


The flow meters show the actual activity in the respective loop. If the actuator is shut down, then there is no activity in that loop so the relative flow meter will show zero - in a poorly assembled system it is possible - but very unlikely - for a slight reaction.

Yes, you can screw down the actual flow meters but ONLY use the nut to do this. Preferably use a ratchet ring spanner to avoid breaking the glass. If the flow meter has been properly adjusted it will only need 2 full turns or less. The maximum number of turns on most flow meters is 3 so be gentle! DO NOT USE THE GLASS PART to screw it down. In some systems, the glass can be turned slightly to seal it properly.

Depending on the quality of the actuators you MAY not have to remove them, simply shut them down.

If anyone installs a system without a filter - they are around £100. - they must be crazy! Admittedly, a properly flushed out system with APex pipe is not going to accumulate much debris, but why risk it?

I agree that there should not be so much debris as you describe. Maybe the pipes were not cleanly stored. However, although you describe the coloration as red/brown, it may be that the main blockage problem is the Algae I mentioned with it's natural green colour being dominated by the debris.

I think what you are going to have to do is FIRST put in a filter (preferably Fernox TF1); Isolate the manifold and make sure there is no serious blockage in both flow and return; reflush the system using a cleaner (Fernox F3). Flush out one loop at a time, closing it down again while you flush all the others. Don't forget, flush through in the correct direction. Also, check the filter after flushing each loop. Then, finally, use a inhibitor (Fernox F1). When fitting a Fernox TF1 be careful with the screw fittings. The filter body is plastic and the brass nuts can easily cross thread.

If the amount of debris is very great, you might be advised to disconnect each loop return pipe from the manifold (after shutting the valve down!) and using a hose pipe to extract the flushed out liquid. In this case, do not use the Fernox F3 until you have finished so that you are not wasting it. You will, of course, be using a hose pipe to supply the flushing water through the manifold fill point. This is an extreme action and other more experienced engineers may have a better suggestion.

Your comment that a different two loops failed puzzles me. It is possible that the original system was underpowered and/or inadequately balanced. It is unlikely, but possible, that the flushing would transfer a blockage from one loop to another. How did you carry out the flushing?

The following link explains flushing fully. http://www.fernox.com/problem+solving/how+to+sheets/cleaning+a+central+heating+system
Taxes, again thanks for your very helpful response.

Okay so i removed all of the flow indicators but unfortunately i was unable to get into the glass part to clean around the spring. As you can see from the below picture they are still very dirty.


After cleaning as much as i could i replaced them ready to flush each individual loop again. The below picture shows the manifold with the electric actuators removed ready for loop flushing.


I,m now starting to think the main problem is the balancing. NU-HEAT supply a very could drawings package complete with flow meter settings. However due to the amount of **** and the fact that a few of the meters are jammed i do not think the system is balanced as per design? New flow meters will be getting purchased.
Ill also be looking at installing a filter, i may need some help on its location though as this system does not look as straight forward as mine. LOL.

Ok thanks again Taxes.

Oh yeh forgot to mention all loops were individually flushed again.

It looks like all of the debris is out now.


Excellent photos! One picture saves a thousand words!

They are standard flow gauges. To remove the glasses, grip them tightly by hand - possibly using a rough cloth to increase grip - and unscrew them in the normal anti clockwise direction.

The system looks normal (apart from the untidy electrics!)l. The filter should be located on the return pipe from the manifold to the heat source. I assume that the process is Heat Source - Pump- Manifold Supply - Heating Loops - Manifold Return - Heat Source

I forgot to say that the flow meter adjusting nuts are set a fully open but I notice that the flushing pipes are still attached. I assume that you have reset them by now.
Yeh adjusted everything as per the design drawings but like I say because some are clogged up with debris I don't think they can be trusted. New ones coming tomorrow.

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