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

 

[Knappers]

I'm glad you went to the effort but it was more the advice to turn the gas valve on and off that I take issue with!
It's not even a usefull test for the consumer as obviously turning off valve will stop the issue regardless.
If you hadn't mentioned the letby then I'd probably not have picked up the issue but the idea of considering a significant amount of letby and not advising shutting off permanently (especially on a premix burner with open venturi) is dumbfounding!

 

[Knappers]

I suppose atleast now the OP can put his multimeter to good use😱

 

[oz-plumber]

HI Knackers,

Most parasitic flames are cancelled by the high limit thermostat.
Generally, the consensus is a gas valve fault.
Secondly, PCB Fault.
Thirdly - Fame sensor fault.

If you read through the Baxi Technical Manual - ( not the boiler installed ) - but generic through most boilers.

Change PCB - if this does not rectify problem, change gas valve.
Change Gas Valve - if this does not rectify problem, change flame sense electrode.
Change flame sense electrode!!

Generally, I start with the cheapest option - Flame Sense Electrode - and this 8 times out of 10 fixes the problem.

Understanding boilers operations, that is why I suggested turning off the gas valve when not in use.
My understanding from the OP was that the boiler shut down on 'overheat', which stopped the gas to the burner.

That is why I suggested turning off the gas valve when not in use.
If I thought the problem was more serious than that, I would have suggested turning off the boiler completely.

Thanks for your informed comments

 

[Knappers]

I wouldnt be quoting texhnical manuals for consumer advice.
Each to their own oz-pumber 😋

 

[oz-plumber]

FYI Knappers - All available online
You don't have to search hard to find anything about any boiler.

Most of the UK spare parts supplier have boiler manuals online - available for anyone to look at.
Including fault finding and service manuals.

Oh...and then there's Youtube...............

 

[Knappers]

OK dude 👍
All the best to the guy with the problem.
Please don't be tempted to change a gas valve or get stuck into your boiler - testing parts.
If you suspect a serious issue with your boiler or even if you have to regularly reset a fault, please seek professional assistance from a gas engineer - in person.
A lack of hot water is not normally potentially life threatening, just a bit of an inconvenience.

If you fancy making a rotating belt of knives tho then I think that's a cool idea and can point you at a YouTube video that shows how to do it😁

 

[oz-plumber]

Post the link to the video........Dude!!!

 

[Knappers]

🤣
Must be OK😁

 

[Bob6464]

Thanks for the replies and help all, had no hot water for a few days but new boiler is being installed tomorrow, i have always been happy to descale plate heat exchangers with spirit of salts but i do not have the skill or knowledge to go further than that, so decided to live with cold water for a few days rather than mess with things that our beyond me.

Thanks Again

 

[oz-plumber]

Thanks Bob6464,

Tried to help you as much as I could without getting into too much trouble.
All of the solutions provided are freely available on the net.

My point was that you could have hot water for showering / bathing if you manually switched the gas valve at the boiler on and off at / for your convenience. PITA, but, you could at least have a hot shower and heating sporadically when required.

Apologies from me - and I don't speak for the forum, about the Knob - Knappers, who in his own right took it upon himself to have ago at me for trying to give you some help and sabotage your post.

I went slightly off track also, posting information freely available on the net.
Obviously some of the information, on your situation in particular, he has or had no knowledge of.
Sharing information - helping others..........I hope I gave you some assistance.

We're here to help each other, if I crossed some line, I haven't been informed as of yet......still waiting.

I haven't looked at Knapper's video he posted, if it had something to do with Plumbing I may have.
Did you? - Did it help your boiler issues?

Over and out,

Hope your new boiler gives you years of trouble free hot water & heating.

Oz

 

[Bob6464]

Thanks Bob6464,

Tried to help you as much as I could without getting into too much trouble.
All of the solutions provided are freely available on the net.

My point was that you could have hot water for showering / bathing if you manually switched the gas valve at the boiler on and off at / for your convenience. PITA, but, you could at least have a hot shower and heating sporadically when required.

Apologies from me - and I don't speak for the forum, about the Knob - Knappers, who in his own right took it upon himself to have ago at me for trying to give you some help and sabotage your post.

I went slightly off track also, posting information freely available on the net.
Obviously some of the information, on your situation in particular, he has or had no knowledge of.
Sharing information - helping others..........I hope I gave you some assistance.

We're here to help each other, if I crossed some line, I haven't been informed as of yet......still waiting.

I haven't looked at Knapper's video he posted, if it had something to do with Plumbing I may have.
Did you? - Did it help your boiler issues?

Over and out,

Hope your new boiler gives you years of trouble free hot water & heating.

Oz

No criticism from me mate, as you said you were only trying to help, new boiler is up and running so all is well, thanks again all

 

[Knappers]

No probs Bob.
Glad it all worked out well for you in the end.
🙊