Potterton Suprima 60 HE boiler in hot water only mode

[mike_r1958]

Hello, I am fairly new here, so any answers gratefully received.
When in HW-only mode the boiler burner operates for approx 1 minute and then turns off for 2 minutes (pump is running the whole time) while the hot water tank heats up. Is this inefficient or normal operation? There are no fault lights on the boiler. Thanks.

 

[MrGassafe]

Check motorised valve(s) working correctly.

 

[mike_r1958]

Yes I’ve checked that the 3 motorised valves are all working correctly and the hot water from the boiler goes only to the cylinder coil when in HW mode. All other heating circuits stay cold. The pump is set to speed 2 (out of 3). What seems to be happening is that the flow temperature from the boiler rises rapidly when the burner is on, the burner stops firing after less than 1 minute when the flow temperature reaches about 70degC. The pump continues running while the flow temperature slowly falls, and after another 2 minutes or so the burner ignites again for 1 minute, and so it goes on until the HW cylinder temp reaches the set value on the thermostat (about 65degC. I just wondered if this on/off cycling is normal efficient operation for a boiler, or not?

 

[DP]

Yes I’ve checked that the 3 motorised valves are all working correctly and the hot water from the boiler goes only to the cylinder coil when in HW mode. All other heating circuits stay cold. The pump is set to speed 2 (out of 3). What seems to be happening is that the flow temperature from the boiler rises rapidly when the burner is on, the burner stops firing after less than 1 minute when the flow temperature reaches about 70degC. The pump continues running while the flow temperature slowly falls, and after another 2 minutes or so the burner ignites again for 1 minute, and so it goes on until the HW cylinder temp reaches the set value on the thermostat (about 65degC. I just wondered if this on/off cycling is normal efficient operation for a boiler, or not?

Feel the two pipes at the cylinder for temperature difference
Older cylinders ( with red jacket) had indirect coil that was suitable for Gravity flow so boilers did what yours does ( only in that case there was no need for pump to assist circulation). Fast forward changing the boiler that needed fully pumped connection.

Now the assisted flow through the cylinder meant the return to boiler was getting hot as heat transfer to cold water in cylinder slow ( cylinder being for gravity circulation)

Most cylinders now have coils that will heat water to 75% duty in much shorter time.

If the return on your cylinder is cold, there could be a blockage in the tee at the cylinder. Also check for air lock.