Removed radiator - now boiler will not fire

[Rodders]

Good afternoon,

Apologies if this has been asked/answered else ware - I have had a thorough search but just not quite found the answer!

I removed a radiator at the weekend - by shutting off the mains water, turning off each valve, removing the radiator and then draining each side of the system. I have not yet reattached a radiator, but have attached isolating valves at each end to be able to bleed them if necessary.

To cut a long story short once the water was turned back on the boiler will not fire and the pump is making a very weak noise. I am assuming I have an airlock.

So far I have checked the following;

1. All rads have filled up and have been bled (a lot of air came out)
2. The large cold tank in the loft is full
3. The smaller tank in the loft has plenty of water in it
4. All taps/showers etc are all working fine

There is a drain cock on the cold pipe entering the boiler which has water in, but difficult gauge the pressure, and further along this pipe before the pump is an AAV. I have removed the red cap but no air is escaping. It is however quite corroded, so I'm concerned it may be corroded shut if that is possible.

Should/could I loosen the AAV unit entirely with a spanner to allow the air to pass directly? I will obviously then get a plumber in to replace at a later date.

Any help would be greatly appreciated - luckily its a mild autumn so far!!

Thank you
Chris

 

[ShaunCorbs]

I would say can you drain / is there any drain off points boiler end ??

Sounds like it's air locked to the boiler

 

[Rodders]

Thanks for your reply.

There is a cold water pipe coming from the tank in the loft, down into the garage. This then goes through a pump, then there is the AVV, then it goes down the wall into the boiler.

Just before it enters the boiler (literally 6 inches before) there is a drain cock.

Are you suggesting I drain the system from here? Should I turn the water off to the house to drain fully?

 

[ShaunCorbs]

As close as to the boiler as possible, or maybe drain down again and install some on the flow and return pipework

 

[Rodders]

I've linked a hose to the drain cock and water is coming out into a bucket. There are a lot of bubbles, which I assume is the air escaping.

I have not turned the water off so the water will never stop coming out - do I just keep going until the bubbles stop?

 

[ShaunCorbs]

Yea give it a bucket or two and then try it again eg the boiler

 

[Rodders]

Drained for about 30 minutes, still bubbling and the boiler still wont fire.

Going to try and unscrew the large nut on the pump to try and bleed that if possible? (its a Grudfos Super Selectic)

 

[ShaunCorbs]

Yea large nut on the front

Not uncommon for a pump to be bad also

 

[Rodders]

So the bubbles wont stop when draining from the boiler - and when I then go in the loft the small tank is filling and feeding into the pipe that feeds the boiler and sucking a load of air in.

I think it may be time to call a plumber!

 

[JCplumb]

I removed a radiator at the weekend - by shutting off the mains water, turning off each valve, removing the radiator and then draining each side of the system.

So you closed the valves, removed the rad, then drained down ''each side of the system''
Step 1 and 2 were spot on, step 3 wasn't needed and is probably why you now have problems.
If you do this again, you only need to close the valves and whip the rad off. That is unless you need to drain the system to solder an otherwise live pipe, but if it's to decorate or swap a rad like for like, stop at step 2.
If it's off for any length of time and you have a TRV you need to use a decorators cap on the TRV, or cap it with a 3/4 compression cap and rubber or fibre washer.

 

[Ric2013]

Sounds to me like you're draining faster than the ballcock can refill the system. Air in the hose could well be coming from the draw-off cock to which you are attaching the hose rather than from the system. Draining for half an hour to remove air is overkill anyway. A well-designed system will usually self-vent or have enough air bleed points that this sort of thing isn't a problem, but you may be unlucky.

 

[moonlight]

Is the pump running?

 

[Ric2013]

Yeah, could be seized if it's making a very weak noise. I'd be tempted to have a look...

 

[Rodders]

Morning - thank you all for your responses.

I reset the boiler last night and it fired up for about 5 minutes and automatically shut down. The hot water pipe exiting the boiler was red hot, but after a while the cold feed started to get hot - this hot water then started to back up into the garage and right back to the pump. I'm assuming the water is not being pushed to the boiler with enough force?

I shut off the pump this morning at the valve and removed the pump - when I crack the valve there appears to be water pressure behind it.

Ric2013 - when I was draining at the boiler with all the bubbles, I ran into the loft to look at the header tank. As you said, the ballcock was open and water was feeding into the tank, but at the same time water was being drawn from the tank (at a faster pace) and so the exit pipe was not fully submerged and water and air were both pouring in.

I assume this is what is introducing air to the system?

...or the pump is done!?

 

[Rodders]

Apologies, I may have my terminology wrong. When I referred to the header tank I meant the smaller of the two tanks. The larger tank is full.

 

[Ric2013]

That's okay, I'd probably call it a header tank too. The modern technical term is F & E, or feed and expansion cistern.

To be honest, I'm not so concerned about the air as, if the pump is able to push the water around, the air usually finds its way to the top of radiators or out the vent. My first bet is that the pump has seized due to debris etc. Have you tried removing the bleed screw and spinning the shaft with a flat screwdriver? - if you switch the pump on, it should be spinning fast.

 

[Rodders]

I have removed the bleed screw and it doesn't look particularly clean - it does however spin fast when the hot water is turned on.

 

[jtsplumbing]

I have removed the bleed screw and it doesn't look particularly clean - it does however spin fast when the hot water is turned on.

Could still be the Pump ! although spinning the impeller could be jammed or broken off shaft Try a new Pump.

 

[Ric2013]

A lot to spend though if the pump isn't at fault...

 

[Rodders]

So I've tried firing up the boiler and turning it off manually after a few minutes, then repeating several times just to try and push some water through the system.

The boiler fires up ok, but still sounds like water is trickling in the pipes, which makes me still think air, but then a knackered pump not pushing the water along may create a trickle too. Also with the hot water backing up suggests there is no pressure shoving it through!

I guess it can't hurt to put a new pump on it...at least it rules that out!!

 

[SavageW]

From where your cold feed enters to the garage,then pump and boiler is this a long horizontal run of pipe work to the boiler? Any air vents/thumb vents if so on this run? Definately just sounds like an airlock which can be stubborn as f@£k sometimes.Try running the system an slightly cracking one of the pump valve unions to the pump with a bucket or rubble sack to see if you can clear air from the pump/pipe work this way
Also remove the pump head (pump valves isolated) an check the impellers, if half full of sludge use pin or pair tweezers to rod through every impeller to make sure it’s clear an the pump is actually circulating

 

[mache]

You might just have a system that is a pig to bleed, mine is and takes a while to shift airlocks. To get mine moving I need to fire in short busts, sometimes literally seconds and can hear a slug of water move in the pipe. Switch off, let it settle and hear the next lot of air bubble through, then same again. It does work and once done is fine and just bleed in the normal way.
Might be worth you trying something similar

 

[Rodders]

Hi all, just a quick update.

Replaced pump - the old one was full of sludge and red rusty water. Initially the boiler fired but then as before the pipe feeding the boiler got hot and the boiler shut down. I then fired up the central heating system and it gave out a massive gurgle followed by the sound of rushing water. The rads stayed on all evening and all got very hot.

Only problem was when I turned off and tried the HW on its own, boiler lasts 5 minutes and shuts down again. I assume I have a blocked exit pipe between the boiler and the tank? Otherwise I cant understand why the water wouldn't be pushing trough the boiler.

Thank you all for all your help...definitely getting warmer!!

 

[JCplumb]

Sounds like it.
If you can get a strong magnet on the pipework where the cold water from the loft tank is teed into the main heating pipes, you'll probably find that the magnet is attracted to the pipe.
It's an indication of ferrous deposits in the pipework and a likely blockage.
Also check the pipe that will tee off near your zone valve and then goes into the cylinder, that's probably blocked up.
Best fix is to cut out and repipe imo.
On the bright side, you're on the way to sorting this out.

 

[Rodders]

Just to add a little more to the puzzle...

When fired up together, we do get hot water, albeit heating up very slowly - would this mean that there is no blockage? The pipe leaving the boiler and entering the cylinder (mid level) goes through a gate valve and a 2 port valve (set to auto). These all get red hot when the CH is on, as does the pipe that tees off before the 2 port valve and appears to rejoin the pipe that leaves the cylinder on its way to the boiler.

Is it possible to have air in the cylinder that would prevent the hot water entering the cylinder (after the 2 port valve)? Only weird thing is that we are able to draw cold water out of the cylinder, which suggests its full!!

I know I'm going to get a plumber out and he fixes it in 2 mins and charges me £200!!

 

[Ric2013]

Sorry for lack of detail and inability to think, as very tired. But...

Cylinder almost certainly indirect (google 'indirect cylinder diagram') so the fact that you are drawing water does not prove there isn't air in the coil.

And I don't think a plumber will fix it in 10 minutes if it is a blockage.

 

[Rodders]

So the 'hot return from the boiler' is red hot, so I'm happy the boiler is working. This pipe is hot right up to the point of entering the cylinder.

Is it possible that air in the coil will prevent hot water entering the cylinder (and therefore returning to the boiler), and the hot water is backing up and running down the bypass valve which goes back to the boiler. So all the boiler is doing is circulating the same piping hot water (and eventually shutting off).

So final question; how the heck do you get air out of the coil? Was thinking of unscrewing the hot water feed into the cylinder, to hopefully let out air and no doubt a little bit of water?

 

[Rodders]

So I just fired up the HW. The hot return from boiler got piping hot instantly, right up to entering the cylinder. The bypass going back to the boiler got instantly hot, suggesting hot water was going back to the boiler and the pipe exiting the cylinder (going back to the boiler) got pretty hot pretty quick.

Surely that must mean HW is flowing through the coil?

 

[Ric2013]

Assuming the hot water going to the coil is pumped uphill, there could be some air in the coil which would tend to settle to the top, but because the system is pumped, water could still be entering the coil and going down by gravity, fighting the air running back up on the way. Loosening the nut at the entry to the coil as you have suggested might just work. I'd be surprised if the coil itself were blocked.

Sometimes there is a 'balance' gate valve on the pipework to or from the coil that may be mostly shut, but could now be blocked with gunk that shifted during the draindown? If so, may be worth opening fully and letting some flow through before putting back to how it was.