Potterton Performa 24, CH ignition goes on and off in a loop

Thanks for you help guys.

Hi Ben,
the order numbers are also different. See items 131 & 135 from the image attached.

Hi Josh,
if it was an ignition fault, why does the DHW work ok?
If the temp sensor was faulty (i.e. measuring higher temp than the real temp), the boiler would stop & wait for 3min before restarting again. The issue I have is that it ignites on /off every 10sec or so.
 
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does the boiler have a primary flow switch/ or does the pump run only for heating? as it's intermittent it could be tricky to idagnose

if the heating thermistor was faulty then the boiler may not be on anti-cycle mode - depends - worth checking when hot though the resistance of it (turn power off before testing though) obviously
 
You need to compare the ch sensor and the dhw sensor, not the overheat stat.
 
...If the temp sensor was faulty (i.e. measuring higher temp than the real temp), the boiler would stop & wait for 3min before restarting again. The issue I have is that it ignites on /off every 10sec or so.
Logically speaking: yes.
The problem is that you can not test the board without a test bench so the only other options are part changing at random or eliminating all other options.
 
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what do you mean a test bench bengasman ? :oops:

it sounds a weird problem - as suggested though try the sensor swap or maybe replace the board but it could be costly
 
Hi Ben,
I haven't been able to find a separate sensor for CH and DHW. The diagrams only show one single sensor (no. 24 on the diagram) which is used for both modes of operation. Am I missing something?



Hi Josh,
do you mean whether there is a diverter valve? There is one which directs the water to be heated to either be the CH water or run in a closed circuit when doing DHW (see diagrams below). I would say the pump runs all the time on either CH or DHW, since it is the same circuit apart from the plate exchanger.
I will check the resistance of the thermistor at hot when in the boiler. I have checked it outside of it, with hot water, and the value was around
4kohm.

 
Hi Josh,
yes, there is a microswitch which is actuated by the diverter valve. I have checked that microswitch and seems to work ok. I also bypassed it with a wire to double check and the fault was still present.

My question is...what mechanisms can stop the flame in a boiler?
- Temp sensor
- Overheat thermostat
- Microswitch
- Flame detector
- Which ones have I missed?

All of the above are used when in DHW mode and it works fine, so I woulld have thought they are ok as well, when operated in CH mode.
 
is it ok all trhe time on hw?

i'd say thermistor or board fault then

how did you test thew microswitch on thw diverter valve?
 
My question is...what mechanisms can stop the flame in a boiler?
- Temp sensor
- Overheat thermostat
- Microswitch
- Flame detector
- Which ones have I missed?

There are various causes, but some would not re-attempt to ignite, and some would go to lock out.
 
Hi Josh,
on DHW is OK all the time.
I checked the microswitch which is actuated by the diverter valve by simply doing a continuity check and actuating it manually. As I said, for double checking I bypassed that microswitch with a wire (i.e. all the time connected) to see if that was the issue, but the boiler kept on switching on/off in the loop.

joshjames wrote:
when heating is required is there a flow switch that activates ignition?

No

The microswitch is actuated by a pin which comes out of the diverter valve when heating is required. Normally the pin is inside the diverter valve when no CH is required, but it sticks out actuating the microswitch when the CH is activated.
 
Have you actually measured the NO and NC contacts on the DHW demand switch?

Thats a very common fault on those boilers.

Did you really have "zero ohms" on something? If so then your house must be at absolute zero!

Tony
 

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