# Boiler Modulating Query

#### mosaix

Hi

Some years back I had a Worcester Bosch 30CDI boiler installed and this was ideal for the size of house and when the family lived at home and for when they all come and visit at Christmas.

Now there's just the two of us and we only heat the rooms we use and a hot water tank. Consequently, the boiler fails to modulate. With the current temperature setting the boiler heats up quickly to around 70 degrees, turns off, cools down to around 40 degrees and then fires up again. This can't be good for the boiler components (I'm on my third fan) and it probably isn't running at its most efficient.

Will adjusting the boiler temperature and / or pump speed encourage modulation?

Thanks in anticipation.

If you have a hot water tank why don’t you just set the temperature to 60C?

If you have a hot water tank why don’t you just set the temperature to 60C?
Would that make any difference to the modulating?

It's quite simple, if your heat demand is less than the boiler's minimum output then the boiler will cycle, but don't see why you should be on your 3rd fan due to this, the evohome Control system makes boilers continually cycle and I don't see any complaints, oil boilers spend their whole lives cycling, I have a 17 year old Firebird that has never needed any replacement parts apart from the odd service items like the burner nozzle and the braided oil hoses.

With the current temperature setting the boiler heats up quickly to around 70 degrees, turns off, cools down to around 40 degrees and then fires up again.

I suppose the first thing to ask, is the boiler otherwise working effectively. Is it heating the house and the hot water as quickly as normal.

As regards the cycling behaviour, does this happen as soon as the boiler comes on in the morning, or only after the radiators have warmed up. When it is cycling, how quickly would you say it takes to go from 40C to 70C. Are we talking about the region of 10 seconds, 30 seconds, 1 minute, 3 minutes or 10 minutes or longer.

What temperature is the boiler set at.

Last edited:
A relevant feature may be the times that you are setting for heating the rads and the cylinder.

Usually best to have them both on if you are not using many rads.

Has the boiler been serviced properly lately ( to mean checking the minimum gas pressure? )

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