Cant locate airlock - boiler kettling since refill.

[wydths]

I've got a vented central heating system comprising of a Potterton Suprima 40 boiler, Grundfos Selectric pump and unvented HW cylinder.

Last week I lost heat to the downstairs radiators. Bleeding didnt fix this nor was their any air came out of them.

The F&E tank in the loft was pretty sludgy so I decided to drain down, fill with clean water, run for a couple of days before draining down at the weekend to refill with Fernox cleaner.

I had no issues draining the system down and got plenty of black water on the first drain and much cleaner water on the second drain.

Today when refilling I closed all lockshields and TRVS upstairs and filled and bled the downstairs rads first, closing them off at both ends once they were filled just to prevent any possible airlocks.

I then bled the upstairs radiators and proceeded to turn the system on after rebalancing all the lockshields both up and downstairs.

However the boiler must have an airlock somewhere because its boiling and then cutting out. I have bled air and water from the pipe on one of the flow/return pipes at the boiler and also bled air from the highest point in the system which is the top of the hot water cylinder.

The pump does sound noisy but there is water coming from the bleed screw when I open it.

I've spent about 2 hours searching the net and this forum for advice, so apologies if the answer is already here and I just cant find it.

Is there something else I can or should try to clear this airlock? I dont really want to have to drain down again as I'll lose all the fernox cleaner and at nearly £20 quid a bottle its a bit of a hard pill to swallow.

Is there a better way to refill this type of system?

Many Thanks,
Duncan

 

[twgas]

Any lights flashing on the boiler?
Try turning the HW on by itself and the boiler stat to minimum and se what happens.

 

[wydths]

Hi,

The boiler fires and runs - green flashing light as normal. If i leave it to its on devices it will lock out - then the right turns red and flashes and it stays this way until I reset it. I just tried minimum just now - but it was with both circuits on as it was before I checked this post. I will wait and then turn off the CH circuit and give it another go.

Many Thanks
Duncan

 

[wydths]

ok, so I tried just having the HW circuit on by its self and the bolier stat set at the lowest setting but the boiler is still kettlling and cutting out.

What other options might I have?

Many Thanks
Duncan

 

[footprints]

It may well be that the air lock has cured itself this morning often when trying to clear an air lock the water gets loads of small bubbles in it like a fizzy drink, so the pump cannot push well (like air in brakes) but if not it might be worth posting a picture of the boiler and cylinder/pump as without seeing the system it's just a guessing game.

Do the flow & return have a means of venting air where they drop after coming off the top of the boiler? Do you have any auto air vents that have been closed manually or could they be blocked by sludge?

Regards,
footprints

 

[wydths]

Thanks footprints. Everything has switched off overnight so I will go and try it again and see how we get on.

All of my rads on the ground floor have drain points, so I wondered if there was anything to gain from opening them to see if there was any air?

The flow and return pipes to the boiler have one visible drain point fitted - I think its on the flow pipe (would this be correct?) and I did attach a hose to this last night and there was a far amount of air and water combined - then it settled down so I thought I had got to the back of it.

I can easily take photographs for you - but I've lived in this house for 11 years (it was new when I moved in) and had lots of issues over the years so I have better than average knowledge of the entire system.

I cant help think though that there must be another vent point that I have never needed or discovered in the past!

Many Thanks
Duncan

 

[footprints]

Good luck with it, certainly be worth seeing some pictures, I won't be around for the rest of the day so will not be logging if till tomorrow hope for some good news
footprints

 

[huntsoil]

your pump is nackered. replace it.

 

[wydths]

Further info. Having checked the upstairs pipework after the boiler has fired and boiled, it seems no water is getting to the pump or surrounding pipes.

I have re-bled all the rads, pump and highest point pipework but there is no air.

The pump does sound like its making an unusual noise, so given that its 7 or so years old I am wondering if thats the issue.

So as I have insurance cover for this sort of thing, i have called them out and they are coming tomorrow. We'll see what they say. If its not that then I have no idea what the issue is.

We dont really suffer from limescale up here in Scotland and I dont think the sludge was that bad that its caused a blockage. But i may be wrong...

 

[footprints]

Hi wydths,
Yes if your pump has run dry for more than a brief time it's finished, but your first post said it seemed there was water in the pump, a pump that's running dry will sound awful as they rely on the water for lubrication.

It seems likely that you may still have sludge in the system somewhere preventing it filling fully or circulating, so if you have cover that's the way to go as you can spend no end of time trying to get it running yourself and get nowhere.

Please let us know what the engineer finds and how they resolve it.

Best wishes,
footprints

 

[wydths]

Hi Footprints,

Todays update is as follows.

The engineer came out and checked the pump - but he says its working fine. There is still water coming out of it when you open the bleed screw but not very much - he says that he expected more coming through than there was.

He says the noise is because its pumping air and water.

So he said that we have a big airlock somewhere which is preventing the pump from getting the hot water upstairs.

He spent almost 2 hours trying to clear this via the pump, but also via the drain valve on the flow pipe from the boiler.

There must still be sludge blocking the system somewhere because what was happening was that he would fire the boiler up with the drain cock open a little bit. You could see the water wasnt flowing smoothly but instead it was spluttering out - an indication there is air coming out.

Once the boiler cut out, he open the valve some more and the water was jet black. Then it would run clear. Repeat this some 15 times in the hope that it would clear, but to no avail.

He said that he thinks that the main issue here is that the its an open vernted system and as such there is not enough pressure to clear this airlock/sludge and this is a common issue with this type of setup.

He rrecommended that I get the F&E tank replaced with a high pressure vessel, thus converting this to a sealed system.

My next door neighbour has an idential house with identical heating system and he did this a year ago (although I am not aware that he had an issue with an airlock) and says that he notices a huge improvement in the heating system.

So I am convinced this is the way to go and have made a call to a trusted engineer who does work for the family as the insurance are not covering the cost of the conversion. I am not really surprised at this though as i didn't think it would be.

Does anyone know of anything I can do to clear this huge airlock and get my system going? Bearing in mind its had 2 drain downs in the last week and this hasn't worked. Can it be reverse filled from a hose pipe via the boiler drain cock? Or does this risk potentially pushing any sludge blockage somewhere else inaccessible?

The second time it was drained down I refilled like this.

Open all downstairs lockshields and TRVs.
Close all downstairs vents on rads.
Close all upstairs lockshields, TRVs and vents

Open HW Zone valve
Open CH Zone valve

Close highest point vents (on top of the water tank)

Open the ball cock on the F&E tank and let the water in.

Wait for the tank to fill then commencing bleeding downstairs.

Bleed upstairs rads.

Bleed pump.

Bleed highest vent points.

Start up boiler........

Many thanks for the continued interest and advice in this post, it is very much appreciated.

Duncan

 

[footprints]

Hi Duncan,

Sorry to hear you still have a problem.

I'm slightly confused about your drain /refill procedure, it reads as though you are filling with some rad valves turned off unless I’m reading it wrongly. You need all valves inc motorised ones open, bleed valves off and start bleeding from the bottom rads up.

By the vents on the tank I assume you mean on the flow & return into the cylinder, it might be worth opening them from time to time during filling as the cold feed often comes in close to them and it may aid filling.

A blockage is very common at the tee where the cold feed enters the system, this can mean that although water can enter the system it may not be clear enough to allow the system to circulate, the only reliable way to know is to cut out the pipe work and check physically your plumber should be able to sort it out if thats the case. A partly blocked cold feed / vent can also lead to pumping over or air being pulled into the system a common cause of sludge.

There is a theory that as sludge is magnetite formed by rust, a magnet will be attracted to the copper pipe if a large blockage is present, can’t say I have ever bothered to try it though! I just used to plough in with the hacksaw and a few compression fittings to reconnect the pipe.

Getting a reliable plumber to give a quote to sort out the system seems the best route as the system must have a problem to be producing any more than the little bit of sludge in the bottom of the rads that comes out just at the end of draining one.

Regards,
footprints

 

[Andy128]

I had a kind of similar issue last year when I drained down a vented system. When refilling, I bled all the rads, pump etc but the pump sounded a bit dry, so I left it off for a few hours to let the water settle in.

After the wait, I turned the system back on, but with the boiler thermostat set to zero to prevent it from firing. The pump seemed a lot less noisy, so I let it run in CH mode for an hour, and then HW only mode for an hour (switch between CH and HW a few times), before firing up the boiler.

The boiler (an old Potterton 16/22 Electronic), made a few slight knocking noises, as it had probably drawn some crap in to the heat exchanger, but eventually sorted itself out once the Fernox F1 and F2 had worked the magic. It no longer makes any such noises.

Maybe try doing the same, as leaving the pump running cold by itself will hopefully work the air out of the system, and prevent the boiler overheating (so long as the pump isn't totally dry of course!).

 

[wydths]

Apologies for not posting a further update. I have been away with work most of the week and not been online.

So I am still waiting for my engineer to come and visit (time of the year - poor guy is flat out) but there seems to be a strong suspicioun that the air seperator may be blocked/restricted with sludge.

I have taken 3 quick pictures this morning.

1471 shows the pump, and HW zone valve.
1472 shows the seperator
1474 shows the CH zone valve and bypass valve.

So if I suspect that this is the issue, is it just a case of getting this removed? Or does anyone have any suggestions as to how to get it unblocked?

I have tried forcing mains water down the feed and vent pipes and there was a fair amount of sediment coming back up when doing this.

Furtherfore although its very difficult to get any sort of flow, it seems that warm water is trying to get up towards the pump but never gets past the seperatror. The other pipes are stone cold which leads me to this conclusion.

If I remove this, does it have to be replaced with the same thing, or can you somehow attach all the pipes together?

I think it may well be a job thats beyond my capabilites but i like to keep on trying, especially seeing as the weather is so cold just now.

Many thanks
Duncan

 

[footprints]

Hi Duncan,
The air separator is the point where the open vent / cold feed enter the system, as I said this is the most common place for a blockage. For some reason the sludge which is normally, well sludgy, turns into something resembling cement! I believe it is something to do with the cold water from the tank meeting the hot water in the system but physics and chemistry ain’t my strongpoint!

I did manage to partly clear one that was totally inaccessible behind the cylinder by cutting in as close as possible and pushing a bit of curtain wire down the pipe then rotating it with a cordless drill on very slow speed but in truth I think I was pretty lucky. The cylinder and pipe work was coming out as part of a new boiler installation a few weeks later so I had nothing to lose.

Can’t see your piccies but I assume it’s a drum like device with connections coming off, the only sure way is removing the unit and chipping out any deposit with a screwdriver or something similar, best though to replace the unit if you can get the same type, as you will never get it totally clean. Strictly you don’t need one but you do need to know how to configure the pipe work correctly, the air separator with its large chamber and connections helps to sort it out for you.

Depends how good your plumbing skills are, unless you are fairly experienced I would leave it alone and plead with your plumber for a visit.
Also cutting into a system with blocked pipework often leads to a gush of black goo that has not drained out properly