Ideal Isar m30100 cuts out error LF when hot tap turned off

[member]

Hello,
I have an Ideal Isar m30100 which cuts out with error code LF whenever a hot tap is turned off.
A week ago a boiler engineer replaced the flame detection electrode but the problem remains.
The central heating is functioning ok, and when the DHW is running plenty of hot water flows from the hot tap.
When the hot tap is turned off the display goes from d with steady green LED to d with flashing green LED.
After 10 flashes there is a click and then the display shows LF.
On pressing the reset button the boiler fires up and will again supply central heating water and DHW.....until a hot tap is used and then switched off....which causes the cut out again.
The cut out also occurs during the night when the c/h is off. I have not observed it directly when it happens, but I think this will be the preheat which, on reaching the desired temperature, switches off the gas in the same way as turning off the tap. I am not an expert, I am surmising this to be the case, and I may be wrong about the reason for the night time cut out.
If anyone can shed any light on this fault we would be very grateful.
Thank you,
member Sun Dial

 

[tininho]

Hi,

The LF fault is an ignition fault, or flame failure....

My First port of call would be a fan or flue fault.... When running in H/W mode, the fan works at a higher rate than in CH mode, so that the gas/air ratio is higher, thus alowing maximum heat output.... If the fan is sluggish it is possible that the gas/air ratio is out and causing poor combustion and in turn causing the flame failure.... This could also on occasion give an L8 fault code

Other causes of LF faults are: choked condensate trap, faulty PCB and (on occasion), fault with burner or ionisation probe......

Hope this helps,

Martin

PS: The reason the boiler runs through the night (seemingly with no demand) is that the Isar has a built in hot water pre-heat system. In effect, it keeps a small store of domestic hot water constantly....

 

[tininho]

By the way... is it noisy when in operation????......

 

[member]

Hi Martin, Thank you for the information. To answer your question, no, it is not noisy, it does not bang when the gas lights, and no rattles or grinding come from fan or pump, they all seem ok.
To me the significant factor is that it is only when the hot water tap is turned off that the cut out occurs. We can run a bath or long shower with no problem, until the tap is turned off.
I have read that the sensor in the plate heat exchanger detects the drop in temp as the hot tap is turned on (when initially cold water flows), and the rise in temp when the hot tap is turned off (due to no water cooling effect). After the 10 LED flashes it always cuts out at that point.
Thank you for helping with this.
member, Sun Dial

 

[tininho]

It's certainly a strange one..... In theory there is no reason why this should be specific to H/W, other than the fact that the boiler burns at maximum output on H/W op's, but generally doesn't on C/H...... Could be a fault with the Printed Circuit Board.... Difficult to prove the fault in this kind of situation....

Martin

 

[jeza]

Hi,

I am having exactly the same problem with my M30100. I was just wondering if you ever worked out what was wrong with yours?

Thanks,
jeza....

 

[gas4you]

I've only ever had one occurence of this and it turned out to be the condensate blocking slightly.

 

[member]

Hello again,
Yes, it has been fixed.
The problem stemmed from the woven glass insulator around the inside edge of the cast aluminium combustion chamber. The insulation had moved and the flames were licking directly on to the aluminium, it could be clearly seen as discoloured in the front left corner. After a few more days of constant resets it gave up completely. The cast aluminium case in that corner was now dangerously distorted and close to melting, maybe resulting in leaving a hole in the chamber. On this area of metal is fitted the flame detection electrode, and this will have moved position with the distortion.
Anyway, the boiler was deemed to be 'shot', with a seriously dangerous design fault. It was replaced with an Isar HE32 by the manufacturer.
I am still not sure of the connection with turning off the hot tap though, that still seems a strange symptom of this fault.
BG were superb, excellent service. Try a fixed price repair first.
Good luck with yours.