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

 

[RJD68]

Hi again Ric2013. As the 2 offending/cold loft rads have NO air in them (only water comes out when I bleed them) I must assume the air lock is somewhere between the 1st rad on the loft circuit (as this has always worked) and the two others. The pic I posted earlier showing the 90degree elbows taking first floor (copper pipework) into plastic pipe that feeds the 3 loft rads. From the plastic elbows to the first rad (that working one) is about a 5m straight & level run. From this rad to the next rad (which is the first cold one but full of water) is another straight and level 3m run. I'm surprised how the air can always get trapped somewhere on this section and not say in the 90 elbow area. Will an air vent (auto or manual) in the only accessible area (below the 90degree elbows shown on pic) solve this if the air lock is elsewhere along the run ie. over 5m away? Can this air just come from elsewhere in the heating system and migrate up into loft and just happen to always want to 'settle' in this particular area of pipe run?

One other qu. that might be relevant to our loft airlock? We have a tall Bisque rad similar to this
TRB-180-30 - Trubi radiator range - General Radiators
in a first floor bathroom. It's 1800mm tall. It makes a waterfall/running water sound which I understand from Bisque tech people is quite common for these tall rads (so much so that they have a specific tech sheet they send to help customers bleed these style of rads). I can get the air out by way of this convoluted process each year but neverteheless it does eventually start the running water noise a few weeks after having been bled. So might this one bathroom rad on the first floor (which used to be the highest point in the system) be generating air just because of its design and it's this air that's now seeing a higher point to travel to ie. Our loft?

 

[RJD68]

Kop it seems we posted at the same time. We have a Vaillant EcoTec 637 combi boiler

 

[king of pipes]

You most definitely need a auto vent in the tall radiator you may also need to add a extra expansion vessel to the system you could possibly be loosing water when the boiler is heating disscuss this and the above with your installer , 15mmm pipework will only run 2 rads really you may need to sacrifice heat in other parts of the home to improve this hope this helps. regards kop

 

[Ric2013]

Hi RJD,
I agree with you that, if the horizontal run is genuinely horizontal and not dipping due to flex in plastic pipe, it is not that likely to airlock. The new radiators will not be creating air, nor will your bathroom towel rail, although air can sometimes get in through less than perfect joints, valves etc.

3 causes seem most likely (though there are other possibilities):
1. there is insufficient corrosion inhibitor which is creating a build up of hydrogen gas in the system
2. there are various air pockets in the system (plus the air that will always be in fresh water), and the air is migrating to the highest point, and there getting stuck (should be a short-term phenomenon, but can sometimes take months to complete)
3. there is an inherent design flaw in your system that admits air - until now this has settled in the bathroom radiator from where you have removed it, but it has now found another place where it prefers to settle

The point, though, is that it is not acceptable for the air to settle in places in which it gets stuck. If the flow to those rads all comes via those elbows, I wonder if bringing those elbows up half an inch (making an artificial high point) and replacing them with tees with an autovent on the top of the upstand thus created, would allow the air to settle and be removed from here, instead of running further along where it seems to be getting stuck? If it's stupid but it works...

I agree with what others are saying about 3 rads off 15mm pipe (how big are these rads and are they single/double/finned/unfinned?), but would suggest that, even if the pipe sizing were out, I'd expect to see some flow to the radiators served rather than a total blockage, and you said it has worked previously, so it really suggests air rather than lack of flow.

 

[RJD68]

Hi Ric. Installer here now trying to work it out. I agree that the issue is air. As far as the pipe work design is concerned there is an area where the 15mm loft pipework goes over a steel (despite me thinking earlier that we didn’t have that issue) but it’s more a rise and not an abrupt ‘U’ and besides it’s now inaccessible under a wooden floor!! However what’s interesting is that the loft rad that works is fed by a pipe run that comes up from the first floor and goes conventionally/horizontally under the loft floor. Tee’d off this run is the pipe work to the 2 rads (that don’t work) and this pipe run has to rise 2-3” to go over a steel.
So he started by closing down slightly the lock shield on the 1 good operating rad in loft (double finned approx 4000btu) and opened the lockshields on the other 2 in loft (one a towel rail 1800btu and the other a double finned rad 2500btu) and this created some flow and heat to these 2 previously cold rads and also seemed to shift a small amount of air!
So maybe some extra water flow is enough to dislodge the smallish amount of air....if this is indeed possible. (I’m not a plumber but my physics is sound).
However this has been done before and here we are again with the same problem so I am again questioning the design around this wretched steel beam.
From your post it might seem prudent before fitting air values etc and/or an extra CH that we try the easy method of removing air build ups as they occur over the next few weeks/months.

(he was questioning the Vaillant EcoTec pump output but I checked that it is a 6m head pump so man-enough for a loft I’d say.
He was suggesting that with insufficient pump pressure from our ground floor boiler that flow into the loft area might not be sufficient and that any small amount of air in the15mm pipework in the loft might just be enough to throttle the water flow).

When we get fed up with this and decide this hasn’t worked then we move on to the air valve &/or extra pump.
What’s your view of installing a greater capacity pump to ‘push’ the water up to and around the loft with greater efficiency and power?