Ariston A/23 euro combi, intermitant fault

[drivewasher]

My son has an inherited Ariston A/23 combi, full new system looks to be about 2 yrs old.
Spark generator gets no supply when it won't light (240 Volt), and after a few seconds lock-out lamp comes on, when it does ignite it gets about 136 volts ac. Tested everything I can think of. Fan and venturi OK air switch operates gas valve opens but not always a spark when I say spark I know it's not the generator as I have volt meter across it's input-no volts,well 2 or 3v ac
If I put a big screwdriver on the pump and bang with my hand the vibration through boiler makes the generator spark and hey presto all ok, on CH gas valve modulates as reaches temp, and burner goes off when it want's to re-ignite most of time it's as above needs a gentle tap (pardon the pun)
Fan runs ok, air switch does operate every time, gas valve operates every time but obviously when no flame detected lock out comes on.
The flow reed switch closes every time even when it won't ignite. Pump is free but i've felt better, can't be pump as it wont even light when stone cold, so not an overheat,and as I said reed switch closes every time. Any thoughts, I'm a domestic appliance engineer hence no stranger to fault finding, just need to know any quirks re fire up sequence I may have missed
Thanks in advance

 

[Agile]

I am not sure which switch you are refering to.

I think that that model may have a system water flow ( not DHW ) flow switch which MAY be the fault. You should measure the voltage across it which should fall to zero when its activated.

Its tapping the pump which makes me suspect this although its not competely logical from what you say.

Tony

 

[Gasguru]

Assuming you have an A23/MFFI

I have seen this fault before - traced it to poor relay contacts on the right hand side circuit board (power distibution).

Suggest you follow spark gen. cabling back to board.

You will need serial number of boiler as there are several board versions fitted. (not cheap either)

 

[drivewasher]

Yes it's an A/23 MFFI,
Just sorted it, I suspected faulty relay also, so I took board off (240v board) and traced the relay for sparker, no dry joints visually obvious when checked before, relays are selaed lid type so tried to lever lid off with small screwdriver against the board, the 240v switch pin pulled out from board track along with a nice round lump of solder, a nice dry soldered joint.
Removed relay, cleaned terminals and track re-soldered, all working beltin

 

[Paul Barker]

I had same fault on a Genus last week, bridged out the flow switch and it fired up, so jumped to the conclusion it was the flow diaphragm, and ordered one. In the event it only worked occasionally, the fault turned out to be that relay you mention. I ordered new board cost about £70.

I gues the a23 and genus share quite a few common parts from the look of them.