LOFT CONVERSION done BUT 2 out of 3 loft rads not heating

[RJD68]

I've had the installer back for this one already so want to try to get as many facts from the experts as to what might be going on.
New loft conversion, Vaillant EcoTec 37KW boiler on ground floor with UFH in kitchen and 13 rads + the 3 in the loft.
Rad feeds for loft have been taken off the rad circuit on first floor and go up into loft. According to the installer, due to the steelwork in the loft the plastic plumbing pipe runs had to go 'over' one of the steels (as it couldn't go through it of course) then back down into the loft floor void. I estimate the the feed pipes had to go over a 20cm high steel if that helps.
After installation and testing all 3 rads were working however after the heating was switched off (not needed due to time of year) 2 of the loft rads stopped heating. They are both downstream of the first one on the circuit that has always worked.
The rads (one a conventional convector rad the other a towel rail) were stone cold as were the rad pipe feeds to them. Bled both rads but NO air coming was out of their bleed valves, only water.
Plumber returned and said this was caused by the bend in the plastic feed pipe producing an air lock as it was going over the steel. He came and sorted that (didn't see what he did but he did say there was air trapped in the system) and then all 3 were working again.
A few days ago the 2 downstream stopped heating again, and as before with no air out of any of their rad bleed valves, only water.
Interestingly this time though the pipe feed to the TRV of the rad immediately downstream of the one that has always heated was hot hot but the one from the lock shield was cold. So, it seems as if some hot water has managed to get from the first rad on the circuit to this one, ie. better than last time it failed. (Note that before when the 2 rads failed their pipe feeds [TRV&Lockshield feeds] were both stone cold).
So, anyone got any ideas what's going on here.
Is it a fault in the pipe run design with the pipe going over the steel? If so can this air lock be sorted by way of an air valve on this pipe? If so what are the implications on the pressure in the boiler system overall if air is continually venting out of the sealed system?
OR might it be that the installer simply hasn't bothered to balance the system?
My concern is that seasonally as the central heating is switched off we will get this air lock (if indeed that's what it is) every year and will need a plumber out each time to sort it which isn't acceptable.
I've yet to pay the final loft build instalment so with some help from this forum as to what might be going on I will have stronger grounds for withholding final payment until this is well and truly sorted.
Thanks, over to the experts.....

 

[The Marnix]

It could well be the pipe running over the steel work is an air trap. Though of course it may not be air it could be hydrogen if the system if the system is in a state of decay. Make sure you have inhibitor in the system to stop this. Whoever installed the system should have treated it and should be able to tell you what inhibitor they have used. Not all inhibitors can be mixed together so don't just put anything in, it may act against what already in there.
Cutting an automatic air vent into the pipe that is becoming air locked should stop that from occurring. This should be neither difficult or expensive and I'm sure whoever installed the system would be more than willing to do this if you are withholding a completion payment.

 

[ShaunCorbs]

Don't suppose you have any pics of the offending pipes ?

 

[Vee]

Could also be air ingress in addition to having a high point where air is being trapped. Are there automatic vents elsewhere on the system?

 

[Ric2013]

You could fit an auto air vent on the inverted U, but, quite honestly, I'd rather have a manual one (less to go wrong) as once the air is out of the system, it normally stays out, especially on a sealed system so you'll probably never need to use it again. Especially if it isn't an 'open-vented system'.

On a newly filled system there are often airlocks and air tends to find its way to the highest point and settle out. In your case, it probably causes a blockage in the process. You'll probably find it will be absolutely fine once the airlock has been cleared a couple of times though. If this weren't a new install, I wouldn't be insisting on changing it, but, as it is, manual air vent would be good practice. Or auto airvent.

Agree with Shaun though: pictures would be good. Otherwise we can only be vague as we can't see the situation.

 

[RJD68]

Thanks all. Looking at the photo (as opposed to what the installer told me about the pipes going over the steels) it's clear that they come up from the first floor then via a 90 degree bend go under the loft floorboards and not over the steels. So, can air build up with this type of pipe installation? As for auto air vents I don't think we have one. Having said that B.Gas installed a valve on a heating pipe near boiler some years back as the Vaillant was losing pressure. This device has a gauge which was set on it and serves to simply maintain boiler pressure which we were losing at that time causing boiler cut outs (it turned out the pressure loss was due to a leak in a CH pipe, now repaired). However, I don't think this is a vent valve as Marnix & Ric2013 mentioned. The pipes shown in photo are now inaccessible behind a dwarf wall in loft but could an air vent be placed in the pipe run from first floor to loft (which is accessible in a cupboard below) or must it be in the highest part of the system? Where or what is the inverted U Ric2013?
As for inhibitors, yes he put it in but he never checked or asked for compatibility so not sure if that's the issue here?
Thanks for help so far, any further advice about balancing maybe??

 

[justlead1]

Have they balanced the system after the additions?
Have you tried turning all the unaffected rads off and monitoring the result on the offending rads.

 

[Old Account]

As above really, did you try balancing the system? Basically turn the rads off which are working to force all the heat into the ones which don't work

 

[RJD68]

As above really, did you try balancing the system? Basically turn the rads off which are working to force all the heat into the ones which don't work

 

[RJD68]

I'm pretty sure the installer hasn't done that so thanks for that advice, that's where I think I'll start before considering cutting in air valves etc. Thanks Matchless.plumb

 

[justlead1]

I do not know how handy you are, but you may be able to try.
Topping up the pressure
Turning off all rads.
On the last on circuit (One that not working) turn off both lock shield and hand wheel valves and remove 1/2" BSP plug or air valve at top of rad. Screw some thing 1/2" Bsp that you can connect a short length of hose to. Once the hose end is in a bucket turn on one of the rad valves, this should pull a lot of water and air through. ( you will see it, in terms of a splutter.) Turn off valve and try the other, same deal as above.
Put the plug back and turn rads on again.
(once a system has been drained and filled there will be pockets of air all over the system. Which will rise to the third floor, which means you may need to repeat.
Good Luck

 

[RJD68]

Thanks Justlead1, that sounds very much like what the plumber did the first time the 2 loft rads stopped working. I'm just surprised that so much air can find itself back into the system such that 2 rads go cold again after just 7 days or so. Maybe that's to be expected?? If the plumber can't come back right away then I'll follow your advice and give it a go myself. Thanks.

 

[Ric2013]

To answer latest question, the air shouldn't be getting in, but it might just have shifted within the system.
By inverted U, I meant that if the pipe runs uphill and then down again (like a U upside down where we thought it ran over a steel) air will tend to collect at the top of the upside-down U, or at the highest point. It is at this point that an air vent might be needed. Air vents elsewhere may be useful, but I meant specifically at the highest point where the pipe goes up and then back down. I meant this or this:

End Feed Air Vent Cap 15mm x
Bottle Air Vent 15mm

That said, I once (before I was a plumber) installed a system where pipework ran up from a manifold on the ground floor into pipework under the first floor boards and then dropped to radiators. One pipe run up and down again for each of 3 radiators (inverted Us). Once the initial airlock was cleared in commissioning, they did not ever airlock again.

Sometimes a system simply does airlock several times before it settles into reliable service. You can sometimes turn off every radiator other than the offending one and you'll hear the bubbles force themselves into the top of the radiator from where they will now be easy to bleed out and then it will get hot. Works best where there is a pump separate to the boiler that you can temporarily set to maximum while you do this.

But should not be a regular occurence and most installers would be happy to solve such teething problems for you, I think.

 

[RJD68]

Thats very helpful. Much appreciated Ric2013

 

[RJD68]

Had the installer back yesterday. He balanced the whole system from ground floor to loft and that has solved the problem. It wasn't another airlock after all which was a relief. Thanks all for helping sort this.

 

[RJD68]

2 weeks on from the balancing and the same 2 rads in the loft are cold again. So balancing didn’t do it. Any suggestions as to the best course of action, is it:

a) better to try to remove the airlock one more time.
Is it reasonable to expect air to lock a few times before all the it’s all finally purged?

or

b) as the air been removed once already and the problem persists might it be better to install an automatic air valve and be done with it?

If b) as we can’t now get access to the top of pipe run (it’s concealed in loft) we can only get access to the pipes that run up to loft from a cupboard below anyone have any suggestions as to how to get an air valve installed at the top of the pipe run? Is getting the valve ‘near’ the top of the pipe run OK and better than having no valve at all?

 

[king of pipes]

Fit some of these they will keep you system vented , check a good quality inhibitor has been added and raise your working pressure to 1.5 bar cold and around 2bar working pressure when hot . cheers kop

 

[RJD68]

Thanks kop, I’ll show this valve to the installer when he comes on Monday.

 

[Ric2013]

If the rads were filling with air, an autovent would be great, though wouldn't address the underlying defect. But, if the pipework itself is airlocking, I can't really see how it helps. KOP - can you please explain your logic, out of interest?

 

[king of pipes]

My theory is, this is a add on to the existing system so it would have been drained and refilled hopefully with a good quality inhibitor added to avoid hydrogen gas forming, when refilling the system via the filling loop there will always be air introduced into the system through oxygenated water it will take several days or even weeks to release this the heating process will cause the trapped air to rise collecting in the highest points of the system forming a air type plug in the pipework which the heating pump will struggle to overcome if you can realese this trapped air and balance the system correctly then you stand a better chance of the system working the Aladdin auto airvent will aid this process i usually still fit a manual vent in the other side of the rad , and also run the system at a higher operating pressure 2bar when fully heated , the op has not said if his boiler is a combi , or system boiler but i would guess it is one or the other so the pump will be internal to the boiler so you are stuck with what you have there are are methods of improving this but i would try the above first . regards kop