Can anyone help - banging pipes

Our neighbours have a BM2000 fitted (worked OK for the last 8 yrs) and despite various plumbers and engineers looking at the system, they cannot fix it,

When the BM is switched on everything seems OK with the display LEDs etc. However, when the boiler kicks in, everything is OK for about 30secs then the pipes above the boiler bang and the boiler cuts out.

I thought this maybe an airlock, but surely the BM is self venting thro the tank?

The BM is upstairs and the boiler down stairs.

Any ideas, as they have been without heat and hot water for over a week.

Thanks

Check the boiler pump is working.
Vent it see if turning.
Check the F & R from the unit to boiler.
Could be a blockage.
The boiler is firing then overheating by the sound of it.
Also drain some water from the unit. And check the unit is taking water from the F & E tank.
Could be low on water/ blocked cold feed.
Pumps need to be the correct ones as in Grundfos.
Mike
MGC/H2O
Norfolk.

Hi Mike
The boiler pump is working, can feel it turning when you remove the big screw from the front.

The flow from the boiler (LH pipe as you look at the BM) gets extremely hot, but the return to the boiler is stone cold when it comes out of the BM and then obviously at the other side of the pump.

All three pumps are Grundfos.

The BM seems to take water from the tank when the boiler kicks in and then returns it to the tank when the boiler trips out.

Any ideas?

Yes all what I said in last post.
Try all and see
Mike
MGC/H2O
Norfolk

Thanks
How do you check f&r from boiler? Is there an easy way to do this?

I'm fairly sure that the flow from the boiler is OK, as when the boiler starts, the water in this pipe gets extremely hot, but the return out of the BM is cold. This would suggest a blockage inside the BM?

I have drained some water from unit using the drain point at the PHE.

If the boiler pump is ok.
And because you can hear it running.
Or feel it turning when you remove the vent screw.
It could be the impeller is not turning.
You could turn the pump valves off and remove the pump head.
BUT the pump valves will most likely leak, if they do will have to drain the unit to fit new valves.
Or it may be the unit is blocked.
Or the return to the boiler is blocked.
Drain some water out of the unit from the drain off at the bottom of the unit.
And see if the unit takes water from the top tank.
If the boiler has any drain off points you can try draining at that point.
You can buy sludge remover, but if there is no water movement then it will not work.
You may have to drain the unit and remove the return connection and try from there.
All the above can be very time consuming.
And remember when all done add a litre of inhibitor to every 100 litres of water in the unit and system.
Mike
MGC/H2O
Norfolk

OK
Took pump head off and impeller spins OK.
Turned off water to f&e tank, drained water from unit using drain point below phe, level in f&e tank went down. Turned water back on, tank filled up.
Disconnected return pipe above boiler and drained water in pipe, was slightly coloured but no real signs of sludge.

Put everything back together , turned boiler on. The return pipe above the boiler got hot(?) then pipes banged, boiler tripped then flow pipe got hot. When boiler trips you can hear water entering the f&e tanks.

What do I do next (apart from have a beer?)

When you took pump head off.
Did you open bottom pump valve?
When you drained boiler pipe. Did you check both?
Did the return get hot before the flow?
Is the heat getting from the boiler to the boilermate pump?
Or is the return getting hot first?
Mike
MGC/H2O
Norfolk

Took the whole pump off and then took the head off, so don't know.
Yes drained both pipes from BM to boiler.
Yes return got hot before flow.
There is no heat getting to BM pump.

Sounds like Flow is blocked.
Or the pump is us.
Did you try the pump with it out?
Have you disconnected the flow and return on the BM?
What about a hose on the boiler drain off?
Be nice if there is one on the flow!
Mike
MGC/H2O
Norfolk

There is no drain on the pipes above the boiler, so I guess I'll have to drain the BM (using the drain valve below the phe) and then determine if the flow and return pipes are clear.

The only other drain is on the he within the boiler, but I think i would be quicker draining the BM and then draining the f&r pipes between the BM and boiler.

Tomorrow going to be fun...

I think someone has recently changed the pump, so I think that will be OK and didnt look blocked when I had it apart

Should be a drain off on the bottom of the BM.
You could try swopping the boiler pump with the heating pump to try.
If not get it drained and the boiler to.
Put some DOC's on the boiler flow and return whilst at it.
Try clearing the pipes from unit to boiler.
You may be lucky with drain worm.
Or if not try hose to drain and out side tap.
It is all trial and error.
How long is a piece of string.
Best get lots of beers in!
Good luck!
Mike
MGC/H2O
Norfolk

Well, drained the BM, disconnected the f&r at the boiler and at the BM.
Proceeded to pour water down flow pipe at BM (to check if pipe was clear) and it came out the return pipe!! Some nugget had crossed the f&r pipes in the BM during one of the previous attempted repair.

Uncrossed the pipes, put everything back together and heh presto, heat and hot water.

One of the alledged experts quoted them £1000 to repair. Time for a career change me thinks.

Well done.
Not always simple is it!
Mike
MGC/H2O
Norfolk