PUMA 80..SCALDING HOT WATER THEN COLD.

[Heating one2one LIVE]

HELLO EVERYONE,
I'M NEW TO BOILER REPAIRS(I'M AN INSTALLER).THIS IS MY FIRST POST.I POSTED IT IN THE WRONG SECTION 1ST OF ALL.PUMA 80(PERMANENT PILOT) FIRES UP FULL FLAME FOR HOT WATER.THE BURNER DOESN'T MODULATE DOWN TO LOW FLAME AND THE BURNER FLAME CUTS OUT.THE WATER GOES COLD AND THEN THE BOILER IGNITES AGAIN...THE CYCLE GOES ROUND AND ROUND.I'VE TRIED DISCONNECTING ONE OF THE LEADS ON THE MODULATION ON THE GAS VALVE WHEN RUNNING THE HOT TAP AND THE FLAME CUTS OUT THEN GOES TO LOW FLAME.I HAVE CHANGED THE H/W THERMISTOR AND THE USER DISPLAY BOARD(BOTH DONE NOTHING TO HELP).THE POTENTIAL DIAL ON THE FRONT OF BOILER FOR THE H/W HAS NO EFFECT WHEN TURNING UP OR DOWN ON THE FLAME?THE PRESSURE IS GOOD ON THE HOT WATER SIDE(I KNOW IT'S A COMBINED HEAT EXCHANGER AND THIS COULD BE THE PROBLEM?)I'VE NOW CHANGED THE MODULATION MAIN PCB AS WELL AND STILL THE SAME PROBLEM.IF THE HEAT EXCHANGERS SCALED THEN THIS WOULDN'T EFFECT THE FLAME(OR WOULD IT)?I'M VERY NEW TO BREAKDOWN SO FORGIVE MY KNOWLEDGE AND ANY SILLY POINTS I MAY HAVE MADE.THANKS BRAD.

 

[BingoBongo]

youve replaced both boards and the thermistor?

does the fan speed increase and pump run (dont take noise or vibration as positive movement)

most likely modulator coil on gas valve anyway.

let me know how you get on

 

[kevplumb]

1 WE AINT DEAF

2 don't double post (forum rules)

 

[Agile]

Who is going to pay for all the parts which you have fitted which have not cured the problem?

Fixing boiler is not just changing parts until you find one that makes it work! ( Unless you work for British Gas ).