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Discuss Boiler green light off then back on? in the Central Heating Forum area at PlumbersForums.net

Jurgenjay

Messages
188
Hi all,

I am not sure whether anyone ever saw this issue....

My Worcester Bosch boiler was installed last year August, since then I found the boiler green light (burner light) will be off after HW is satisfied(supposed to be), but after 2 mins it will be back on again! For 2mins of firing, the green light will be off, then after 2mins it will be back on! Throughout this repetitive process, the blue light (power light) is on all the time---i.e zone valve for HW is open all the time.

I called cylinder manufactory Joule to come to check, they extended the copper temperature sensor inside the cylinder temperature box and changed new cable---now the boiler blue light will be off i.e. zone valve will be closed after HW is satisfied (before zone valve never closed, blue light always on), BUT, I find the green light will still be off first, then after 1 or 2mins, it will be back on! Then after firing 1min or 2mins, either it will be off or Blue light off---once blue light off (means zone valve closed), the green light will be off.

To put simply, my issue is: why green light will be off for 1 or 2mins, then back on? Then go off again, then back on, until blue light off, then green light will be off accordingly.

What I know for boiler lights operation is, once zone valve opened, the boiler blue light (power light) will be on first, then green light (burner light) on; When zone valve closed, blue light will be off then green light off immediately----Green light should not off then back on, then off then on.

Anyone notice your boiler has this issue? Or know what could be wrong?

Thanks!
 

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Chuck

Esteemed
Messages
2,613
For S-plan type systems, which is what I think you probably have, the boiler flow temperature needs to be at least 5°C above the set-point on the thermostat that controls the domestic hot water zone valve. The minimum DHW temperature I recommend (for systems that have a single constant flow temperature set-point) is 60°C. So, if your hot water is stored at 60°C, the flow temperature needs to be 65°C or greater.

So, I'd start by measuring the temperature of the DHW to see if there is scope for reducing it. if not, try turning the temperature knob on your boiler up by 5°C (about one division), which should have the desired effect.
 

Jurgenjay

Messages
188
For S-plan type systems, which is what I think you probably have, the boiler flow temperature needs to be at least 5°C above the set-point on the thermostat that controls the domestic hot water zone valve. The minimum DHW temperature I recommend (for systems that have a single constant flow temperature set-point) is 60°C. So, if your hot water is stored at 60°C, the flow temperature needs to be 65°C or greater.

So, I'd start by measuring the temperature of the DHW to see if there is scope for reducing it. if not, try turning the temperature knob on your boiler up by 5°C (about one division), which should have the desired effect.
Thanks for your suggestion!
Actually your suggestion did make effect! I didn't put more details in my original post, what you mentioned I had done all those. The HW temperature in my house is about 60°C, before my boiler temperature was around 74°C----at the time the boiler green light always off/on alternatively & blue light never off, so the boiler was operating all the time.
Now, as I turned the boiler temperature up to around 80°C now, the blue light will be off now (zone valve closed), but green light still back on for 1 or 2 minutes then off before blue light off----previously green light back on and off all the time.
 

Chuck

Esteemed
Messages
2,613
The HW temperature in my house is about 60°C, before my boiler temperature was around 74°C
A 14°C difference should be more than enough for the system to behave properly. Increasing the difference to 20°C is helping by transferring heat more rapidly but is not getting to the root of the problem.

The problem, heat not being removed from the boiler faster enough, remains so the next thing to check is the circulation rate. This could be low due to the zone valve not opening fully, a balancing valve being too restrictive, a clogged filter, weak pump, etc.
 

Jurgenjay

Messages
188
A 14°C difference should be more than enough for the system to behave properly. Increasing the difference to 20°C is helping by transferring heat more rapidly but is not getting to the root of the problem.

The problem, heat not being removed from the boiler faster enough, remains so the next thing to check is the circulation rate. This could be low due to the zone valve not opening fully, a balancing valve being too restrictive, a clogged filter, weak pump, etc.
Thanks again!
"The problem, heat not being removed from the boiler faster enough, remains so the next thing to check is the circulation rate. This could be low due to the zone valve not opening fully, a balancing valve being too restrictive, a clogged filter, weak pump, etc."====all these could be the reason the boiler green light off first then back on, then off, till blue light off?
 

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