Scale problem?

[jpm777]

Hi,

I have a worcester bosch 19/24 cbi. It was very noisy, however after using some fernox f2 this has dramatically improved.

The issue remaining is that when I switched on the hot water, the boiler fired up for initially about 15 minutes, then went off for 3 or 4 minutes. After having been on for about 30 mins, I checked again and found the boiler was only coming on for an ever decreasing amount of time. 2.5 mins on then nearly 4 mins off. This reduced down to 1 min 10 seconds on and 4 minutes off, before the water got up to temperature (60c) after about 1 hour 15 minutes.

My Central heating engineer, thought it may also need a new heat exchanger. Is this normal behaviour or could it be a sign of scale build up on the heat exchange shutting the boiler off so quickly?

 

[45yearsagasman]

It does sound like a circulation problem, but the last thing I would be looking to change is the heat exchanger.
The flow and return temps need to be checked, and pump performance etc.

 

[Agile]

It is normal for non-modulating boilers to cycle on/off when heating hot water.

This is particularly so if the cylinder is old like the copper or yellow foam types which did not have very large heating coils.

Its also possible if this is recent problem that the coil is scaled up either internal or externally or both.

Tony

 

[jpm777]

It is normal for non-modulating boilers to cycle on/off when heating hot water.

This is particularly so if the cylinder is old like the copper or yellow foam types which did not have very large heating coils.

Its also possible if this is recent problem that the coil is scaled up either internal or externally or both.

Tony

Hi Tony,

Thanks for the reply. Is it normal that it cycles so much though? It gets progressively shorter so it's only coming on for around 1 minute and off for 4 minutes which means it takes ages to heat the water up.
The house was built in 2005 and as to whether it is a new problem. I'm unsure as I have only been in the house 10 months and it has always seemed the same.

Pete,
Thanks for your reply too. I mentioned the heat exchanger as I was wondering if it may help. I can get it done for free under my warranty as the engineer has suggested it. I live in a very hard water area if that makes a difference?

Thanks again.

 

[jpm777]

Any suggestions are welcomed !
Just want to make sure I can get the boiler working as efficiently as possible. It seems strange to me that it can come on for as little as 1 minute. It takes well over an hour just to heat water to 60c. It's off for a lot longer than it's on.

Thanks.

 

[jpm777]

Any more thoughts / replies please?