noisy boilermate a-class ov

Hi.
My boilermate a-class ov is driving me potty at the moment.
Basically glowworm boiler cut out and wouldn't re-light , engineer came out and messed around for a bit.
He then went to look at Gledhill as it was banging like boiling water in pipes.
didn't actually touch anything but said replace circuit board.
I bought a new gt490 pcb but it is different in that it has smaller black relays instead of the large clear jobbies and different colour parts at bottom by the fuse. I contacted seller who said " it'll work mate " - it doesn't , just has c33 code for id.
long story short put old pcb back in and noise still there.
Now if the hot water is on constant it spits water back into the tank on top , then suck it back in with a lot of banging ( noise from water ejected into tank ).
boiler in garage lights every 5 mins or so and more noises , but if heating is on constant ( under trip off thermostat temp ) noise is nowhere near as bad , if it trips off due to house temp we have noise again as just hot water boiling.
Water and heating are both fine and hot as usual, just noises and ejecting into top tank.
my original pcb has code c23 , does anyone know what the c23 is?
sorry for the novel , but no one in my area is old enough to have the will to work on a boilermate , so looks like I am left to figure it out as Gledhill not too keen on coming to Edinburgh.

Right.
Have you the book / manual.

If you need one download from Gledhill website.
There may be more than one issue, so check you have the correct one.

The codes you mentioned are in the book.
Along with any ID ref for the ACB
Code 33 is ID ref. Did you set it when fitting new ACB?
Code 23 no idea not in the book. Not all are. May not be relevant to your model

But I would check the boiler pump
1; Has it a supply?
2; Water/ No air?
3; Is it working.

Why?
When you have the heating on water is moving and your problem is lessened

Also header tank has water?
Unit will / can take water from tank? Checked?

Mike
MGC/H2O

Hi Mike.

pump is working.

water is being drawn from tank ( as it is ejected into tank and then re-taken back onto unit )

I am wondering if a temp sensor has failed on the bottom of unit as the temp is way above 80 on one of the readouts - I believe there are 3 sensors? 1 @ top , 1 @ bottom and 1 in the pipe to the pump ?

I may bite the bullet and buy the 3 sensors.

main problem is the gt490 board which is different.

I coded with A01 as per manual , but it still locks out with the c33.

current board is gt490 but has clear relays , not the small black ones as per the new board.

Hi,

Should not be chucking water into header tank
Still sounds like pump or a blockage.
Have you put a hose on the unit, drained it. Check the F & E tank level goes down?

Mike
MGC/H2O

You could try swapping the bottom & middle sensors round.
There are 5 sensors in total

2 x GT198 ref DHW

2 x GT198 middle & bottom

1 x GT 199 overheat sensor

Also as an experiment try turning your boiler down, see what happens

Mike
MGC/H2O

The boiler is turned down to approx 60% to keep the noise of the banging to a minimum just now.

Can only remember seeing 2 sensors on the unit it's self , 1 at bottom right (4 pin ) and 1 at top left (2 pin)

I'll have to have a closer look for the other 2 so as I can swap the middle and bottom.

Thanks for your advise. Much appreciated