worcester 28cdi rsf combi problem

[johnjonjon40]

hi problem with boiler, have central heating(works fine, except pressure slowly increases). But when hot water tap is switched on pressure rapidly increases, boiler overheats in just a few seconds and shuts down. have replaced diverter valve.

 

[nickso]

do you get any hot water from the taps? how long does it take for the boiler to fire up again? is the boiler on a sealed or open system?

 

[Rob]

Plate heat exchanger?

 

[nickso]

Plate heat exchanger?

thats where i was going

 

[evolu]

new expansion vessel required.
seen these rise very slowly on ch mode.on hw mode the high temp of the water shoots the gauge past 3bar.

 

[kevplumb]

new expansion vessel required.

why not check the pre charge pressure first

 

[evolu]

because its lost pressure for a reason,normally a split in the diaphram.
its a sealed unit so pressure shouldnt be lost unless a fault.

 

[kevplumb]

waffle
thats why they tell you to check the pressure after 3 years when servicing

they do lose pressure over time

i suppose you never have to top a sealed system up either

 

[bellairaphon]

id go plate heat exchanger

 

[bengasman]

Checking the ev is 5 minutes work and no parts, replacing it, or changing the hex is slightly less pleasant.