Saunier Duval SD30e - problem with water

[DavidDudgeon]

Hi,

i just moved into a house a few weeks ago and the boiler was working fine. I am now failing to get hot water. I have stripped out the domestic hot water microswitch and tested it, it works fine. However it seems to be the piston that drives the switch that is failing to protrude when the hot water is switched on. I can activate the hot water by manually activating the switch, so switch is def ok.
Is this part of the pump assembly? Is there any known way to repair / test further?

Any help appreciated
Davie

Furthermore i have just discovered that when i run the hot tap downstairs the piston doesnt move. When i run the bath taps upstairs it moves about 8mm - Does this suggest a pressure issue within the switch assembly? Also i have ran the hot water and used pliers to start the piston off and it cycles if you fluctuate the the tap - The issue seems to be unseating the piston

 

[Gasguru]

Replace the diaphragm behind the brass cover. If there's any sign of leakage around the pin replace the brass cover assembly too.

 

[DavidDudgeon]

Hello Gasguru,

thanks for the feedback.

Is the diaphragm just a standard part or will it be bespoke to the Saunier Duval make?

Do i need to drain the boiler to remove the brass cover and replace the diaphragm?

cheers
Davie

 

[Gasguru]

Bespoke Saunier Duvall part (or Glowworm 80E)

Isolate cold water inlet only..10 minute job.