Air in boiler - is plumber giving me the runaround?!

[expertgasman]

[In doing his work, he mentioned that we had ‘no pump overrun’ and did our boiler ever bang (no idea how those two relate)? The next day it started banging!

The hot water has been ‘on’ constantly for the past 2 weeks, but the boiler very very rarely fires – when it does, it bangs within 30 seconds, then stops again – so no hot water (unless we use the immersion).

Did the bathroom gut drain the system, say to move a radiator?
If he didn't, my money is on the pump or cold feed blockage. If theres no circulation, the boiler will quickly heat up and cut off via the thermostat. it will take ages to cool, and the process will repeat ad infinitum. There could also be a blockage at the cold feed connection, and therefore a lack of water in the system.

 

[petit_pablo]

Im not convinced its a circulation issue.

Is there a code that come up on the boiler when it bangs? Icos should put up a code if its overheating. LE normally.

 

[matt1e]

Hi Tony,

I don't think he did - I seem to remember him saying that he could hear the pump running, but that's all.

James

hearing it running is not definitive,it only means the motor is ok, the impeller may have come off as they often do.
I'm with the others on this, I think the boiler is overheating due to circulation problems
either damaged pump or blockage

Matt

 

[James4791]

Hi - thanks again for your comments - really useful.

The boiler doesn't show an error code - just fires up for 20-30 seconds, bangs a few times, then stops.

The bathroom guy didn't drain the system to my knowledge - he did fit a new radiator but it was in the same place as the old one.

thanks again

Andy

 

[IanMichael]

problem lies with the changing of the radiator from your bathroom fitter. air in primary circuit. shut down all your rads then fire boiler up for a few minutes, might clear it.

 

[Boilerman2]

Only just read this post!
a couple of things seem a bit strange to me ;
a) I am suprised the plumber who changed your bathroom noticed you
had no pump over-run, and quizzed you about it asking if the boiler
banged??
b) Straight after he left ..suprise suprise!! boiler starts banging!!!???

c) has this plumber closed or almost closed one of the pump valves
in order to get "more value" out of the job????

Call me Cynical, but i would check that your pump valves are fully open!!

 

[petit_pablo]

Possiby a cold feed blocked if it happened after the rad was fitted. Can you drain a bit of water off from a drain point?

Turn the water off at stop tap and drain some water off. If the water level in the CH header drops cold feed is ok, if the water level remains constant cold feed is likely blocked.

 

[tonybhoy]

Only just read this post!
a couple of things seem a bit strange to me ;
a) I am suprised the plumber who changed your bathroom noticed you
had no pump over-run, and quizzed you about it asking if the boiler
banged??
b) Straight after he left ..suprise suprise!! boiler starts banging!!!???

c) has this plumber closed or almost closed one of the pump valves
in order to get "more value" out of the job????

Call me Cynical, but i would check that your pump valves are fully open!!

Sounds plausible.

Still think it's a circulation problem, first thing I would have done would have been to change the pump.

 

[James4791]

i will try the boiler on with all rads off to see if that works. Not sure how to check if pump valves are fully open??

Does sound like it could be a pump problem being dragged out!

 

[tonybhoy]

i will try the boiler on with all rads off to see if that works. Not sure how to check if pump valves are fully open??

Does sound like it could be a pump problem being dragged out!

If they are the 'gate' type then just try to turn the spindles on the end both valves anti-clock wise but go easy cause if they are open then forcing them will snap them however if they are the ballofix type then there is a slot on the valve for a large flat screwdriver to open or close, in the open position the slot will be parallel to the valve and at right angles to the valve closed.

Be wary of these ballofix type valves though as they leak if you so much as look at them, I would get your plumber to check these ones if I were you.

 

[expertgasman]

Possiby a cold feed blocked if it happened after the rad was fitted[/b]. Can you drain a bit of water off from a drain point?

Turn the water off at stop tap and drain some water off. If the water level in the CH header drops cold feed is ok, if the water level remains constant cold feed is likely blocked.

Seems the most likey scenario

 

[fazedup71]

totally agree, blocked feed.

 

[JohnD]

James, the blocked feed very often shows itself after a radiator has been taken off e.g. for decoration.

What happens is that the pipe connecting the feed and expansion tank gets blocked with sludge or sediment. As the system is already full of water it continues working. When you put the empty rad back, it tries to refill itself from the pipes, but there is a gallon or so less water than is required, because it is not topping up through the blocked pipe. This causes the water level to drop.

Depending on how much water was lost, where the water level was before, and where the pump is in relation to the new water level (especially if the pump is upstairs next to the cylinder), there may be air in the pump, or in enough pipework to stop water circulating.

With no water circulating to carry the heat away, the boiler quickly boils, overheats and shuts down.

The blockage is often very hard with limescale as well as black magnetite, and chemical cleaners will usually not shift it as there is no flow through the blockage. The blocked pipe has to be cut out and replaced.

A very similar problem occurs if the F&E tank is empty due to the ball cock seizing.

The only good news is that yours failed in summer not winter.

Can't be sure, but this sounds like your problem. An experienced heating engineer would have seen it dozens of times so I'm surprised your chap didn't look for it.

I am a householder not a pro

But have experienced both the blocked F&E pipe and the seized ballcock (in different houses).

 

[expertgasman]

James, the blocked feed very often shows itself after a radiator has been taken off e.g. for decoration.

What happens is that the pipe connecting the feed and expansion tank gets blocked with sludge or sediment. This causes the water level to drop.
there may be air in the pump, or in enough pipework to stop water circulating

Can't be sure, but this sounds like your problem. An experienced heating engineer would have seen it dozens of times so I'm surprised your chap didn't look for it.

I am a householder not a pro

But have experienced both the blocked F&E pipe and the seized ballcock (in different houses).

Not quite right, but nearly there. The reason you lose circulation is that the water level drops to the point where you don't have a full circuit of water, therefore it can't possibly circulate.

Try the magnet gig. Get a magnet and hold it where the cold feed joins the system. If there is an attraction, there will be a blockage.