Draining an indirect cylinder to change a faulty zone valve

[GaryN2112]

Sounds like it's not the actuator !

Yeah there's a crack in the metal of the valve body plate as well so I'm just going to replace the body and actuator.

 

[oldbuffer]

That valve is part of the safety system for the unvented cylinder. It should only be changed by someone with a current G3 accreditation.

 

[terryplumb]

That valve is part of the safety system for the unvented cylinder. It should only be changed by someone with a current G3 accreditation.

Maybe you would be kind enough to explain to GaryN2112 how and under what scenario ,the valve can affect the safe working of the unvented cylinder.

 

[GaryN2112]

That valve is part of the safety system for the unvented cylinder. It should only be changed by someone with a current G3 accreditation.

Does G3 apply in Northern Ireland - not sure. Anyways it's my own house not a customer, and everything will be electrically isolated with the boiler fully powered off and drained down - but appreciate the need for the accreditation.

 

[oldbuffer]

Because if it sticks in the open position, it cannot stop heat from the heat source (presumably boiler) continuing to heat the water in the cylinder.

 

[terryplumb]

Because if it sticks in the open position, it cannot stop heat from the heat source (presumably boiler) continuing to heat the water in the cylinder

Given that the water in the cylinder can't get any hotter ( when heated by a gas boiler )than the gas boilers water flow temperature ,why would that be a cylinder safety issue ?

 

[ATTQ]

Given that the water in the cylinder can't get any hotter ( when heated by a gas boiler )than the gas boilers water flow temperature ,why would that be a cylinder safety issue ?

I've just taken an open vented tank out today and realized it can also vent pressure back up the inlet, i guess thats true in these unvented systems as well? Plus temp can't get beyond the gas boilers output as you're getting at I guess. The sludge in the bottom of this tank was disgusting, can't believe we were using it

 

[GaryN2112]

Just to close out this thread - I drained the CH down yesterday and replaced the valve and the actuator (added in some Fernox inhibitor as well). Hot water now functioning as normal again - thanks for all the help, it's much appreciated.