Please Help - CH pipes banging, boiler overheating

[Dixeyboy]

Hi, I would greatly appreciate some advice. I'll try and give as much detail as poss, whilst trying to keep it short.

Boiler: Barlo Balmoral 55F, approx. 15 years old (not Combi type).
Pump: Circulation Pumps Ltd CP53 fairly new.
PCB and Solenoid 1 year old.

Problem: Overheat thermostat tripped and so I reset and fired up boiler. Boiler appears to work as usual, however loud popping/banging of pipes from boiler up to where pump is located. Inconsitent hot/cold flow of water passing through pipe near pump. After less than 1minute, boiler overheat thermostat trips out.

What I've tried so far: System was fully flushed by me and an engineer when I moved in 18months ago, with chemicals. Pump seems to be rotating fine having inserted screwdriver. I have tried bleeding pump and all radiators to no avail. FE tank is full and ball float (excuse my lack of technical terms) is working as it should, so have (maybe naively) ruled out excessive air intake into the system.

Going forward: I have read on another topic, that the heat exchanger may be faulty or blocked causing kettling of boiler and may need descaling. Does this sound like the most likely cause of my problem? I'm assuming a faulty thermostat or overheat thermostat is not the issue, as the pipes are banging and boiler only runs for 1minute before tripping out.

Any advice or help would be greatly appreciated!

 

[Jackrae]

Pump not running ?

 

[Hugh Jaleak]

I would suggest initially this is due to the result of lack of water or lack of circulation. Water is effectively trapped inside the boiler, and so boils rapidly. F&E cistern may be full but is there enough water in the system? Cold feed is usual suspect, maybe blocked. Draw off some water from a drain off and see if the F&E refills itself.

Second issue could be the pump, screwdriver test isn't failsafe, the only way to ascertain if the pump is actually moving the water is to, (Drain down first or you'll get wet. Not recommended to rely on the pump valves to isolate pump.), split the pump and check the impeller is actually rotating and wont stall under resistance.

 

[Dixeyboy]

Many thanks for your reply Hugh. That's interesting, because about a week ago before the boiler issues, the toilet cistern was very erratic in refilling. It seems ok now, but could this be related to a blocked cold water feed and therefore lack of water in CH system? I'll certainly try what you have suggested and and look at the pump also.

Jackrae, thanks for your reply. Very possibly. I'll do what Hugh has suggested.

Thanks again gents.

 

[Jackrae]

Before you strip the pump you can confirm it's running buy :

a) turn down the boiler thermostat to minimum
b) ensure the time programmer is calling for central heating

This should then cause the pump to run as if the boiler was operating normally. By feeling the pump you should feel a slight vibration. If you cannot feel this, try removing the seal screw on the motor body (where you normally turn the pump with a screwdriver). You should then be able to see if the pump is actually running.

If it's not running then either the motor has failed or the boiler controller/pump circuit is faulty.

Alternatively, if your system has zone valves, these might have failed in the closed position and you can "force" most types open by a mechanical lever.

 

[Dixeyboy]

Great, thanks Jackrae! This is helpful. I know for a fact that the pump is vibrating but I suppose I need to take a closer look to see if it's all working as it should.

 

[Hugh Jaleak]

Blocked cold feed is usually due to a build up of sludge in the system. Whilst the system may have been flushed then the cold feed may have been neglected. If this proves clear and the system has adequate water content then look at the pump or a faulty motorised valve as suggested.

 

[Dixeyboy]

Great, thanks again Hugh. Look forward to getting home tonight and having a look.

 

[Dixeyboy]

Ok, so I drained off some water and the F&E tank refilled itself. So I'm looking to take a closer look at the pump now.

Question: Can I drain down the system to just past the pump, instead of draining down the whole system? That way I'm only draining the cold feed length of about 2m + the F&E tank. The reason being, is that I don't really want to drain down the whole system to find that the pump is working fine and it is a motorized valve that is faulty.

Many thanks again! (and apologies if any of these are silly questions)