my sigma 40/60 sometimes fails to reignite when in use - however…

Hi Mike,

The thermostat I referred to is the stat built into the boiler (the one which controls the maximum temperature of the water flowing around the system) NOT the room stat. Its almost as though the boiler does not recognise that the return water is cooler than the flow water and therefore does not ignite the burner until I alter the thermostat setting the flow temperature. Would this make sense? I have checked the pressure switch and tubing.

I should have mentioned before that the boiler never cuts off due to the room stat as we like the rooms hot and they never reach the temperature set on the room stat.

Hi Mike,

Room stat has never cut out as we have it set to 25 degrees and room never gets to that temperature. If I reduce room stat to 21 degrees then it does cut boiler out then when room gets to 21

However the intermittent problem with reignition is not allied to room stat settings, it can happen at any time the boiler is on and does not seem to matter what temperature the boiler stat is set to. However when reignition fails if I move the boiler stat knob though its entire range and back again the boiler usually reignites then.

when you say FLOW TEMPERATURE SENSOR is that the one which screws into the top (flow) pipe which appears to be a thermistor.

Hi Mike I have replaced that item (stupid design as it requires a complete drain down to fit) Problem still persists - it is very intermittent maybe two or 3 times per week. I have also discovered that if I turn to room stat programmer off and on again that will make the boiler refire when it is showing the problem, so will turning the main programmer off and on. It is almost as though the signal to reignite or initiate the sequence is not getting sent by the circuits, when the problem occurs the fan does not operate but the pump continues to run. sorry to take so long replying but when spring came I was no longer using boiler.

yes it is wireless stat, batteries are fresh and situated only about 2 feet from receiver (other side of a plasterboard wall) also the indicator on the receiver shows it has got an active signal. You are the expert but I don't think the issue is related to the stat as the problem also manifests itself when I remove the stat from the wiring. As previously stated issue is intermittent and occurs even when no thermostat is present except the one built into the boiler and a froststat which is there to protect the boiler which is located in the built in garage.

Hi Mike,

no it is not the normal operation. As previously stated it is intermittent.

When the boiler goes off due to flow temperature being high enough it shuts off as expected and then usually comes on again when the temperature of the flow water falls, however occasionally it will not reignite or even operate the fan and then stays off until I either turn the programmer off and on again or turn the boiler stat down and up again when it immediately fires up.When the problem occurs the rads can be cold until I take action as above.

Thanks Mike,

any idea which of the control boards are most likely to be the issue. There are 2 one appears to sense the temperatures, the other one is next to the gas control valve and I think its called the sequence control board. Obviously these are both pricy items so would be a good thing to know which is most suspect.

Ron