Main heat exchanger overheating when heating off

[Bob6464]

Hi All,

Have a peculiar problem with my Gloworm Flexicom 30cx combi boiler, the main heat exchanger is getting red hot and fault coding on overheat even though the boiler and central heating is not on, i shut the boiler down for a while, clear the fault code and it will be fine again for anywhere from 3 hrs to 3 weeks.

We only need hot water during these summer months and i am getting the money together for a new boiler but am at a loss on how it is doing this, when not in fault the boiler fires up and shuts down for hot water demand but then randomly overheats and we lose hot water.

Even though it will be replaced i would love to know how its doing this.

Many thanks for any help and suggestions,

Bob

 

[Knappers]

I'd start by making sure 'preheat' is off.
There's likely another issue but...
Hold + for 3 sec
Press - to turn OFF
'OFF' should be displayed.

See how you get on after that

 

[Bob6464]

I'd start by making sure 'preheat' is off.
There's likely another issue but...
Hold + for 3 sec
Press - to turn OFF
'OFF' should be displayed.

See how you get on after that

Will try that, im letting the boiler cool down at the moment, i left it off all night and the main heat exchanger was to hot to touch and back in fault within 30 seconds this morning

 

[Bob6464]

I'd start by making sure 'preheat' is off.
There's likely another issue but...
Hold + for 3 sec
Press - to turn OFF
'OFF' should be displayed.

See how you get on after that

Pre heat is off, boiler fired on hot water demand but central heating heat exchanger was red hot within a minute and shut boiler down on over temp safety.

How on earth is the main heat exchanger getting hot when no demand is called? loath to spend money on it now as new boiler is 3 weeks away.

Thanks again for any advice.

 

[Knappers]

The main heat exchanger heats the HW one.
Likely HW hex is blocked and that's why it overheats

 

[Deleted member 120897]

If it’s anything like a Vaillant EcoTEC (same group), could be plate heat exchanger, canoe filter, pump, pipework restricted. As @Knappers said, the main heat exchanger (where the burner is) is used for both heating and hot water.

 

[Bob6464]

Thanks for the info guys, always thought they worked independently on the glow worm, will do my best to limp it along till new boiler

 

[oz-plumber]

Could it be the gas valve not shutting off completely?
I've had that on rare occasions.

If you want to make the boiler last for a few weeks, maybe shut of the gas valve when not in use.
PITA, but may be the problem

 

[Knappers]

Could it be the gas valve not shutting off completely?
I've had that on rare occasions.

If you want to make the boiler last for a few weeks, maybe shut of the gas valve when not in use.
PITA, but may be the problem

What the actual....
On occasion I try with this forum I really do!
But come on - really!?!

 

[oz-plumber]

FYI - Parasitic Flame ( generally in Fault Finding in Boiler Manuals )

Copied from Baxi Manual on line

BAXI LUNA DUO-TEC TROUBLESHOOTING GUIDE
16
Version 1
164/
384 Fault flame (parasitic flame).
- Check for proper polarity and grounding to the unit
-Check venting for flue recirculation
-Check wiring connections to the gas valve & PCB – X36 and X2 connector
-Check the resistance of the coils:
Pin 1 and 3 = 20 - 30 Ohm
Pin 2 and 4 = 60 - 70 Ohm
If you do not receive an Ohm reading replace the gas valve. If you get a Ohm reading replace the
PCB
-Check for a dirty flame sensor. It should read 3-5μA when flame is present
-Check location for high winds