This is knocking and water is leaking from somewhere you can't see what's causing it?

[Gary111]

I have an electric water heater which is knocking near the pressure release valve.
It's leaking from somewhere under the bath which I guess may be where the pressure release valve releases to I'm not sure.
Does anyone know what would cause that please?

 

[Gary111]

 

[Madrab]

Oh dear, that's a DIY job if ever I've seen one.

You probably need someone that is experienced with instantaneous heaters/unvented systems. If it's knocking then it could possibly be the pressure relief valve (PRV) that's opening but it's should be a direct connection to a plastic pipe like that. Does it knock regularly?

 

[Gary111]

Hi it doesn't knock regularly, only been doing it when it's leaking

 

[Gary111]

It's still dripping when the heaters turned off which makes me think it's a faulty PRV

 

[CountryFan]

Hi it doesn't knock regularly, only been doing it when it's leaking

Possibly opening and closing on the seating

 

[Nozzle]

I suggest to you it's the sound of the relief valve doing what it is meant to do - (saving the system from bursting through hydraulic overpressure). It's probable the pressure is rising too much as the water is being heated with no-where to expand to. Has the expansion vessel bladder lost all the air?

Nozzle

 

[Gary111]

Thanks, if it lost it's air would that explain water still dripping from the PRV even when the water in the heater has cooled a bit

 

[Gary111]

Possibly opening and closing on the seating

Thanks for your help, what would be the remedy for that?
New Valve?
Or is there something else

 

[Gary111]

Obviously it's been very hot recently which probably has a bearing on it?

 

[CountryFan]

Thanks for your help, what would be the remedy for that?

It needs looking at. Perhaps the expansion vessel has lost its charge, could be a weak spring or grit on the seating.

New Valve?

Depends as I’ve said above.

 

[Madrab]

Is it an instantaneous water heater? 15/30L? Make/Model?

The banging is the PRV doing it's job, the pressure climbs, the PRV lifts, the pressure drops and the valve slams back down. I'd be more concerned as to why it's opening. As suggested that install doesn't seem correct and it really should be looked at by someone that understands unvented systems. or vessel sized dependent, another look at the MI and that install sorted to how it should be.

 

[Gary111]

Hi , what size expansion vessel would you normally have for an 80litre invented cylinder please?
Looks like it's 8 Litree currently

 

[Madrab]

Depends - I wouldn't suggest that your current vessel isn't large enough, though your unvented system and as part of that the expansion vessel probably needs serviced.

When was the system last serviced as that PRV mash up etc should have been identified and rectified at it's last service period.

 

[Gary111]

Around a year ago.