worcester 28 cdi

[gregward]

i have a worcester 28 cdi.when the hot water tap is turned on the the pressure on the "sealed system pressure gauge" goes up to between 3-4 bar and the flame goes out. if the hot tap is left running the "sealed system pressure" goes back down to about 1 bar and the boiler flame returns.
this happens even when the central heating is turned off.
PS
the pressure release valve has dripped for ages!

please could anyone suggest a way to Accurately fault find the problem so i dont get ripped off?

 

[Gasguru]

Is it making a lot of noise? It may be overheating due to trapped air in the heat exchanger or a failed pump allowing the water to boil.

At the very least the expansion vessel is probably flat, the automatic air vent could be blocked or leaking and the safety valve needs cleaning/replacing.

These are not particularly nice boilers to work on and I for one avoid them. It may be easier to call out Worcester on a fixed price repair but check whats not covered first.

Since the pressure is high and you admit you have allowed the boiler to run with faults for "ages" there may be several other problems (especially leaks) and it is difficult to give a price on repairs.

 

[gas4you]

What pressure dose it start off at before tap turned on? Do you mean it starts at 1 bar?

Sounds like it is overheating. What happens when just the ch is turned on for a while?

If this is ok I would look at dhw heat exchanger scaled/blocked.

is the filling link turned off properly? prv should not be constantly dripping

 

[CorgiIOW]

gregward, does the pressure rise when both C/H and DHW is off ! 28cdi s have a integral filling loop. Classic fault of the cdi, is the DHW, heat exchanger, rotting , or cracking internally, so as allowing a constant supply of cold water entering the boiler , IE the pressure will rise, and the PRV will release it . Id be very suprised if the expansion vessel had failed. As others have said, they are not the most straight forward of boilers to work on ,, most, if not all joints, are of 'O' rings, get it wrong , you get wet !

To be honest, they are good boilers , providing they are looked after, IE a service

Please ask, if you are still having problems .

Dave.

 

[gregward]

gregward, does the pressure rise when both C/H and DHW is off ! 28cdi s have a integral filling loop. Classic fault of the cdi, is the DHW, heat exchanger, rotting , or cracking internally, so as allowing a constant supply of cold water entering the boiler , IE the pressure will rise, and the PRV will release it . Id be very suprised if the expansion vessel had failed. As others have said, they are not the most straight forward of boilers to work on ,, most, if not all joints, are of 'O' rings, get it wrong , you get wet !

To be honest, they are good boilers , providing they are looked after, IE a service

Please ask, if you are still having problems .

Dave.

the pressure only rises when the hot water tap is turned on.
if the pressure goes too high the prv releases it.
alternativly the pressure can be reduced by draining water from the radiators!

 

[MikeIsotech]

gregward, does the pressure rise when both C/H and DHW is off ! 28cdi s have a integral filling loop. Classic fault of the cdi, is the DHW, heat exchanger, rotting , or cracking internally, so as allowing a constant supply of cold water entering the boiler , IE the pressure will rise, and the PRV will release it . Id be very suprised if the expansion vessel had failed. As others have said, they are not the most straight forward of boilers to work on ,, most, if not all joints, are of 'O' rings, get it wrong , you get wet !

To be honest, they are good boilers , providing they are looked after, IE a service

Please ask, if you are still having problems .

Dave.

Hi Dave

I think you might be describing a fault that I have on my boiler. For some time the pressure gauge has crept higher over a period of time. Typically the gauge would rise by a bar over a month or two. I've just got back home after a couple of months away and things seem to be worse. I noticed today that the pressure relief pipe was dribbling and have drained off some of the pressure. Without either heating or hot water on the pressure is rising again. Could this be the DHW heat exchanger breaking down? Will I need to change the over-pressure valve or will it reset itsellf? Is it a DIY job for a capable person? Any help appreciated.

Mike