Boiler short-cycling on HW
- Thread starter JohnD
- Start date
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Firstly the HW cyl stat needs to be at 60C, or VERY close, to prevent any chance of legionella breeding.
Mid to high 40'sC is the perfect breeding temp for the bugs
I would check the flow & return temp at the boiler to see if there is proper flow through the boiler.
Mid to high 40'sC is the perfect breeding temp for the bugs
I would check the flow & return temp at the boiler to see if there is proper flow through the boiler.
I think any of us regulars on here would all agree that you far from the above John.
New condensing boilers should be able to modulate down and just 'tick over' rather than the stop/start of conventional boilers.
Have you checked for any air locks in the HW circuit? Have you tried setting the Alpha pump to manual on high speed to push any air through?
Usually in your system set up, I set the boiler flow to 65C and the HW stat to 60C
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I would not move the cyl stat higher. It should be approx 1/3rd up from the bottom of the cylinder.
Moving it higher will reduce the amount of stored HW you have ready for use.
Thre certainly sounds like a restiriction of some sort on the DHW circuit, personally I don't like reducing the DHW flow to 15mm with modern cylinders, as they tend to need the 22mm flow and return to re-heat the cylinder quickly, especially if they are high efficiency fast recovery types.
I can't help wondering if there has been some type of foreign body accidentally introduced into the HW cyl pipe work, causing a restriction, when the pipe work was altered.
Just another thought, as the pipe work has now been reversed, are there any valves that should have been reversed as well at the same time in this pipe work, possibly now the wrong way and causing a restriction?
Moving it higher will reduce the amount of stored HW you have ready for use.
Thre certainly sounds like a restiriction of some sort on the DHW circuit, personally I don't like reducing the DHW flow to 15mm with modern cylinders, as they tend to need the 22mm flow and return to re-heat the cylinder quickly, especially if they are high efficiency fast recovery types.
I can't help wondering if there has been some type of foreign body accidentally introduced into the HW cyl pipe work, causing a restriction, when the pipe work was altered.
Just another thought, as the pipe work has now been reversed, are there any valves that should have been reversed as well at the same time in this pipe work, possibly now the wrong way and causing a restriction?
It's certainly taking a long time to heat the water up!
A surface thermometer (<£20) would be useful.
You really need to now what the boiler temp is doing at the flow pipe.
If you're quick, you could see what the gas usage rate is during the "ON" times. (See FAQ).
Can you turn the pump speed up, for trials?
A surface thermometer (<£20) would be useful.
You really need to now what the boiler temp is doing at the flow pipe.
If you're quick, you could see what the gas usage rate is during the "ON" times. (See FAQ).
Can you turn the pump speed up, for trials?
If there are no restrictions then I would be looking at the aplha pump. Perhaps it is modulating down too much.
Try it on manual full power again but leave it for say 24 hrs and monitor over this time with a full days HW usage.
Personally I don't like these pumps, only fitted 4 and 2 of these were faulty
Try it on manual full power again but leave it for say 24 hrs and monitor over this time with a full days HW usage.
Personally I don't like these pumps, only fitted 4 and 2 of these were faulty
Thats OK then, earlier boiler used grey ones which failed.
I think your imagined problem is solely as a result of setting too low a differential between the hot water and the boiler flow as you seem to suspect anyway.
I suggest setting the boiler to 70°C and the cylinder to 55°C.
Boilers should be set and forgot!
Tony
I think your imagined problem is solely as a result of setting too low a differential between the hot water and the boiler flow as you seem to suspect anyway.
I suggest setting the boiler to 70°C and the cylinder to 55°C.
Boilers should be set and forgot!
Tony
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