DHW heat exchanger

[confused 2]

I am going to attempt to descale the dhw heat exchanger on my old combi, which side will be the most scaled up, the "tap" side or the other?? I intend to remove it to do it ,is this the best way??

 

[noonespecial]

What boiler?

What is your problem?

 

[chrishutt]

If you remove it, you'll see which side is coated with what. It's most likely to be iron oxides on the CH side, which is not scale.

 

[confused 2]

What boiler?

What is your problem?

It is an old Worcester heatslave 9.24,
No hot water when central heating is off, i have changed diverter valve and main burner is igniting ok

 

[confused 2]

If you remove it, you'll see which side is coated with what. It's most likely to be iron oxides on the CH side, which is not scale.

chrishut I have had it off before, it is not possible to see anything inside, it is a tubular type are the iron oxides removable, if so with what??

 

[noonespecial]

If you get hot water when the heating is on then it is not scale which is causing your problem. Sounds like an internal control fault.

Assume you get cold water out of the hot tap when heating is off?

 

[ollski]

If the heating side is sludged up that means the system is sludged up and will have to be cleaned. Are you saying your hot water is fine when the heating is on and non existant when its off?

 

[confused 2]

Hot water is better when heating is on but cold when off, DHW heat exchanger is a separate unit and gets hot, but does not transfer the heat to the domestic water the hot water is forced down the flow pipe of the C Heating side,
diverter valve is working fine ,same shaft that operates it operates micro switch and this works OK ?????

 

[chrishutt]

the hot water is forced down the flow pipe of the C Heating side,

Your problem is that the diverter valve is faulty! When in HW mode there should be NO flow into the CH flow pipe.

 

[Agile]

The pin which operates the microswitches is NOT the pin which operates the diversion !!!

Why dont you take the old one apart so you can see how it works???

As Chris says its your diverter which is not operating correctly!

Tony

 

[confused 2]

I have fitted a new diverter valve and the problem was the same with the old one.
On the old valve the only problem I could see was that the plastic ring in the end [outlet for flow pipe] that is retained by an internal circlip, was broken.
Any ideas where I might see an exploded diagram of the valve??

Thanks for the help It is driving me mad

PS you were right it is not the DHW heat exchanger I cleaned it today--no better.

 

[ollski]

Here you go:

 

[confused 2]

much appreciated ollski Thanks

 

[Agile]

I have never seen a drawing before. Unfortunately the draughtsman seem to ecome tired and the detail in the lower half leaves much to be desired.

If you look at the level near "18" you will see that the central pin is not contiguous.

The lower half is pushed upwardwards by a spring near the bottom, almost invisible in the drawing!

Its the lower half which does the diverting! This lower shaft "follows" the upper shaft upwards in the DHW mode.

The symptoms indicate that this lower shaft is not moving. As that seems unlikely on a new valve then the next cause might be a blockage in the DHW flow path.

Careful use of a contact digital thermometer by a competent boiler engineer would pinpoint the fault !

Tony

 

[ollski]