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Discuss Cold Towel Rail Fed By Robbens UFH System in the Central Heating Forum area at PlumbersForums.net

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Hi All,

Hoping someone can help with what I thought was a minor problem/easy fix issue with the towel rail in my new-ish house; it is now permanently cold.

I'll explain a bit of background, the system set up and some things I've tried so far... Hopefully I'm missing something blindly obvious but it has had me stumped for weeks and weeks now.

The UFH system is a Robbens Systems UFH setup with a three zone manifold fed by a Glowworm Flexicom CX30 combi-boiler. This is the only heating the house other than electric radiators. System setup below:
Screen Shot 2019-12-02 at 19.21.50.png


So, I removed the original towel rail to replace it with a slightly wider one when redoing the bathroom a few months ago. The original radiator was always warm/hot, so I had no worries about the current system setup/pipework. Thought it was a simple remove old rad, plumb in new rad, fill/bleed, sorted... The new radiator filled up and bled fine and was adequately warm for a good few weeks. It then just went cold. Thought this was pretty strange but knew there were plenty of things to try so I did the following:
  • Tried bleeding any air that might've come to top of radiator - didn't work
  • Tried opening lockshield and TRV fully and leaving it for a while to warm up - didn't work
  • Tried attaching hose to top of rad and forcing water through rad under pressure to clear any airlocks (from both flow and return individually, locking off the other each time) - radiator got warm but soon went cold when hose removed and connected back to flow/return
  • Replaced TRV/Lockshield with Drayton TRV4 set (recommended by a plumber I asked).
At this point I started to look at the UFH manifold/setup which feeds the towel rail and two UFH loops. After speaking to a plumber and him suggesting some things I tried the following:
  • Tried removing the manifold actuator controlling the towel rail loop. As expected this made no difference as that actuator is permanently in the "open" state
  • Tried removing the actuator from the boiler return feed. This made no difference either as when forcing the the two UFH loops hot this opens automatically but the towel rail stays cold
  • Tried locking off the two UFH loops and flushing the Towel rail loop with garden hose feed in and hose back out (pretty sure I had the lockshield/TRV fully open when doing this but cant fully remember). Once flushed for a while and sounding like no air coming out/through I re-filled system, bled manifold and towel rail. Towel rail still cold. The UFH worked after refilling and bleeding manifold etc.
During some of the above the towel rail randomly heated up to a lowish temperature then promptly went back to not working.
A family friend fiddled with the lockshield (loosened it right off) the other day too and the radiator warmed up for about a day but then promptly went cold again...

So I'm pretty stumped... The strangest thing is that it was all working fine for a while and then suddenly nothing.

Any questions/thoughts are more than welcome as I'm struggling to get any plumbers to come and have a look at this!

Thanks in advance,
Chris
 
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Did any air come from it when you bled it?
Bled which part? Manifold had some air in after flushing and radiator had some air after emptying and re-filling - both as expected. No more air in either. Towel rail still cold.

Are you sure towel rail actuator is opening fully and connecting with end switch to bring boiler on?
The boiler doesnt seem to be coming on with the towel rail actuator open, no. I actually removed the actuator from the towel rail loop and gave the pin a push up and down to check it was 'free' and it seemed to be. However the return pipe does always seem to be noticeably cooler on the towel rail loop than the two UFH loops.

Pictures of ufh manifold please.
Definitely forgot to add the picture!
20190506_153108.jpg
 
then you need to check if it is wired in to bring on boiler it may just be wired in as a heat sink
Hmm I don't think that is the case. The towel rail was hot all of the time before it stopped working and I havent touched any wiring. I did check it though (finding any info from Robbens seemed very difficult) and it seemed to stack up/make sense. Edit: however I'm no expert so I'm not 100% sure!?

Maybe I should just get a plumber in but that is proving difficult due to let downs/being ignored.

Any other suggestions?
 
Sorry for the confusion earlier PlumbBob, I misread the initial Intel. I have little experience with your type of system, which is why I've held off from commenting further but no one else has piped up so I will speak. After reading your details and looking at the images again I'd be suspect of the towel rail actuator head. Water much like electricity likes the path of least resistance, if you partially close a lock shield or valve or completely close one you are generating a resistance and the water wont circulate (I suspect you will have a little heat in towel rail flow out of manifold but not further). You've proved the rad is full as have you that it's free of air and the valves on towel rail are open, so having said that, like above I'd be suspicious of the manifold valve. You said you took the head off and checked spindle but have you checked to see if you're getting 230 volts to it? This could be a fault in the wiring centre, a loose connection etc. You said this actuator is constantly open so like GasMk1 said above this circuit is most like a heat sink, meaning its constantly open but not wired in such a way to bring boiler on. If you're competent with a multimetre check to see if you have a feed. Also if you take the head off, bring the boiler on and manually hold spindle in open position you might find it starts to circulate. Again UF heating and manifolds aren't my speciality but it's worth a try and of course I might be wrong.
 
Sorry for the delay in replying and thanks for the suggestions SJB.

I've somehow figured out a lot of stuff since seeing your post and trying things!!!

  1. I don't have a multimeter currently but got the trusty old electricians screwdrivers out and used that to buzz out various connections. It proved that all actuators are getting 230V to them.
  2. The above also allowed me to double check which thermostat is connected to which actuator/zone/"room". Turns out the written on the wall was incorrect!
  3. Through doing the above I found that the TS715 programmer is ACTUALLY for the towel rail loop. This seems obvious now but I didn't realise to start with and thought it was an overall controller for the whole Robbens control board!
So by switching on and off the thermostats and buzzing them out I could prove that each actuator was working and doing what they should. Realising that the TS715 programmer controlled the hot water was good too as now, I've programmed everything correctly which the pump is not running all day everyday.

Not sure but by finding out/doing all the above, the towel rail started to heat up. Whether I free'd up a sticky valve on the Robbens manifold or setting the towel rail programmer to not be on 100% of the time has made a difference, I'm not sure...
A curious thing I did find was that the "return" pipe from the towel rail was always hotter than the "flow" pipe. This made me think that the TRV valve was on the wrong side, however after just swapping the valves over, I'm not so sure as when I re-filled the system, opening the original "flow" side (now a lockshield) it filled the radiator up under pressure. This makes me think this is actually the flow side afterall.

I still have some questions I hope someone can help with though:
  1. Why would the towel rail return pipe be hotter than the flow?
  2. The flow from boiler and the return to boiler pipes that connect to the manifold are joined by some sort of pipe (balancing? Looks like it is meant to be there etc), would this affect the above?
  3. I'm using Straight Drayton TRV4 valve/lockshield and to me, the lockshield valve and the TRV valve look exactly the same. They also have a singular directional arrow on them rather than a bi-directional arrow. Does the orientation of these valves REALLY affect the flow in/return out when they're fully open? I've not much experience with this.
  4. The Robbens control board has a DIP switch for different temperature setting (30, 45, 60 degrees C) so this combined with the towel rail programmer would pretty much do the job of the TRV would it not? It would also stop the pump being able to pump against the TRV valve when it was closed, which seems correct, rather than trying to pump against a "dead end"?
  5. Finally, the UFH manifold has no flow meters on it to help balance the system. Currently all three zones are open as much as they can be which also seems odd to me. Fitting flow meters might be a good idea?

After all this rambling, you may be wondering why I swapped the valves round when the towel rail seemed to be working but I really want to understand the setup, not just have the radiator working haha.

Cheers,

Chris
 
Your actuators are on the return of the manifold, the pipe/pipes that don't have actuators are the flow. Yes single direction valves must be installed correctly.

Edit. Terminal screwdrivers are dangerous and a multimetre is the tool to use, it will prove you have both live and neutral, using a terminal only proves voltage on phase wire. Also you may have live and neutral to an actuator but that doesn't mean motors etc are ok.
 
Last edited:
Your actuators are on the return of the manifold, the pipe/pipes that don't have actuators are the flow. Yes single direction valves must be installed correctly.

Edit. Terminal screwdrivers are dangerous and a multimetre is the tool to use, it will prove you have both live and neutral, using a terminal only proves voltage on phase wire. Also you may have live and neutral to an actuator but that doesn't mean motors etc are ok.
Yep, had worked that out already re: the actuators. I wondered if on the flow side of the manifold whether installing flow meters would be useful as these are used to help balance the whole system.

I realise terminal screwdrivers are not the ideal tool to use but as I said, no multimeter currently. I also visually confirmed that all actuators open and close when called to by the control board, which they do. I forgot to write this above.

As the orientation of single direction valves does matter, I'll make sure these are correct now, especially as I've confirmed which is the flow side of the towel when re-filling.

Any other answers to the above would be good though, might even help someone else out in the future!

Cheers,
Chris
 
Yes I cant answer your other questions as I have little experience with UFH like I said but I will follow this post to see if others comment, hopefully like you said I will learn something
 

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