Dripping 6 bar pressure relief on 10liter unvented under sink heater

[Riley26]

needing to swap a 6 bar pressure relief as the one that in in is leaking slightly be it won't reseat with operating it for abit. Probably a stupid question but can I just swap for a 6bar pressure relief from the merchants? There not specific to the under sink heater? I have done all my exams will have my g3 unvented ticket in a few weeks.

 

[Steelmasons]

G3 ticket is not required.

 

[picasso]

Check the expansion vessel (if there is one ) first.

 

[Riley26]

Check the expansion vessel (if there is one ) first.

Thank you, not sure it had one but I'll check. This could of lost its charge and not taking up the expansion causing the pressure relief to run abit?

 

[Roger928]

This could of lost its charge and not taking up the expansion causing the pressure relief to run abit?

Yes or maybe none fitted at all.
But you say..

be it won't reseat with operating it for abit

Were you cranking it open and now it won't reseat?
Probably sediment on the seating surfaces.
Is there a pressure reducing valve fitted also?

 

[Madrab]

Yup, 2 things to check 1st. Supply pressure, if it's exceeding 6 bar, fit a Pressure Reducing Valve. If no EV, what length of uninterrupted cold supply pipe is there to the heater inlet from its iso valve or another cold outlet/draw off, needs to be at least 3m to allow for expansion.

 

[Riley26]

Yes or maybe none fitted at all.
But you say..


Were you cranking it open and now it won't reseat?
Probably sediment on the seating surfaces.
Is there a pressure reducing valve fitted also?

Yup, 2 things to check 1st. Supply pressure, if it's exceeding 6 bar, fit a Pressure Reducing Valve. If no EV, what length of uninterrupted cold supply pipe is there to the heater inlet from its iso valve or another cold outlet/draw off, needs to be at least 3m to allow for expansion.

Thanks I'll check was a pressure reducing valve at about 3 bar but don't recall seeing an expansion vessel. Is it unlikely to it just start leaking cause the washer has gone in it?

 

[picasso]

If there is no expansion vessel then the expansion is being taken up by being forced back down the mains pipe, if a water meter has been fitted or someone has fitted a check valve then the safety valve will be opened when the water is heated, find out why the safety valve opened in the first place before changing it.

 

[Riley26]

If there is no expansion vessel then the expansion is being taken up by being forced back down the mains pipe, if a water meter has been fitted or someone has fitted a check valve then the safety valve will be opened when the water is heated, find out why the safety valve opened in the first place before changing it.

Thanks yes and there should be a check valve to stop expansion back down the cold mains. The valve was just dripping slightly. It could need an expansion vessel fitting then?

 

[Steelmasons]

Do these units not use the supplied ventilated tap??

 

[Dan Robinson]

Not always. Some of them want a loop of pipe to absorb the small volume. Others seem to rely on the crappy flexi hoses (Quooker/Zip etc)

 

[Madrab]

Do these units not use the supplied ventilated tap??

There are 2 types of instantaneous HW heaters (as against the under counter boiling HW heaters)

One is unvented - uses PRV's (relief and if needed reducing), an uninterrupted supply pipe length or EV for expansion, the other is vented - that one comes with a special tap that vents (drips) into the basin as you mention.