Biasi 24s overheat switch tripping

[blooto]

Hi,After use the overheat switch trips but not while the water is running.

The dhw temperature gauge shows 70 degrees with water running but rises to over 80 degrees when it is turned off and then there is a banging noise,the needle on the gauge jumps and the overheat switches in and there is steam escape from the outlet at the top of the boiler. Two weeks ago I put Sentinel x200 in the system,on the bottle it states that it can take 4-6 weeks to work through.

Should I give it another couple of weeks to see or could there be another problem?

 

[kevplumb]

check the h/w flow switch

View media item 15143

 

[Agile]

You have two faults!

A blocked plate heat exchanger.

AND

A ( lime ) scaled main heat exchanger.

OR

A sluggish to retract diverter valve. Perhaps more likely this or both problems!

Its not the end of the world! We often retrieve boilers like that and the total cost is usually under £160 in our local area.

Tony

 

[kevplumb]

You have two faults!

A blocked plate heat exchanger.

AND

A ( lime ) scaled main heat exchanger

tosh

A sluggish to retract diverter valve.

possibly

 

[Agile]

If the plate heat exchanger was totally clean then the temperature on DHW would not be as high as 70° C.

Tony

 

[kevplumb]

and if the main h/ex was scaled it would be dropping out a lot sooner

 

[Agile]

If the main heat exchanger is scaled that is not obvious during actual operation of the boiler, apart from any kettling noises.

The o/h stat is operated by the water temperature.

When the boiler turns off there is not pump over run. If the main HE is scaled the flame side fins have over heated due to the poor thermal transfer and that latent heat is transferred into the water which causes the o/h stat to trip a few seconds AFTER the burner goes off.

Tony

 

[blooto]

Should I introduce Fernox DS3 to the system or will this make no difference? Also what am I looking for with the diverter valve and flow switch that will indicate that they are at fault?

 

[Agile]

You could turn off ALL the rads and then put some DS3 into the boiler and run it on hot water and central heating for 2-3 minutes on each for 10-20 minutes ffor each dosing. Then drain out and repeat. Often 3-5 times.

I actually isolate the boiler and introduce it only into the boiler.

DS3 is not very soluable so you will have to dissolve it in warm water.

What comes out will at first be very cloudy but will clear as the boiler gets cleaned.

But before you do that see if the flame goes out immediately a tap is turned off as the diverter may be slow to retract.

Tony

 

[Homesafe]

You could turn off ALL the rads and then put some DS3 into the boiler and run it on hot water and central heating for 2-3 minutes on each for 10-20 minutes ffor each dosing. Then drain out and repeat. Often 3-5 times.

I actually isolate the boiler and introduce it only into the boiler.

DS3 is not very soluable so you will have to dissolve it in warm water.

What comes out will at first be very cloudy but will clear as the boiler gets cleaned.

But before you do that see if the flame goes out immediately a tap is turned off as the diverter may be slow to retract.

Tony

how is this done it would be good to know Mr.T.

 

[Agile]

Trade enquiries in the CC please!

 

[Homesafe]

DIY'ers could have learnt something from this aswell, Mr. T.

same question in CC now with quote an all

 

[Agile]

If you knew the answer then you would not be expecting me to post it here!

Tony

 

[Homesafe]

point taken.

 

[blooto]

You could turn off ALL the rads and then put some DS3 into the boiler and run it on hot water and central heating for 2-3 minutes on each for 10-20 minutes ffor each dosing. Then drain out and repeat. Often 3-5 times.

I actually isolate the boiler and introduce it only into the boiler.

DS3 is not very soluable so you will have to dissolve it in warm water.

What comes out will at first be very cloudy but will clear as the boiler gets cleaned.


But before you do that see if the flame goes out immediately a tap is turned off as the diverter may be slow to retract.
Tony

The flame does turn off as the water is switched off,so does this indicate a scaled heat exchanger?