pressure release valve on water heater

[pmx_super]

Hi,

I've been told that the replacement unit for my dead undersink electric water heater is one that requires fitting of a seperate temperature/pressure release valve. The old unit had this built in. If I can just plug-and-play new for old I can do it myself so I was wondering what is this thing for and what might the implications of not fitting it be?

I guess it's incase the water thermostat goes and the water boils it gives it somewhere to go. The old unit was installed so it would pour out into the cupboard under the sink , though when the engineer/plumber who told me it was beyond repair saw it he wasn't all that alarmed. What volume of liquid could spray out of one one of these valves?

Cheers,
James.

 

[ChrisR]

WHat volume of water is in the heater?
On vessels up to 15litres I've only seen pressure relief valves, not temp and pressure ones which are required on larger vessels, but you need to check with the manufacturer.
The discharge has to go outside, safely but visibly. It could be a dribble, but it could be a jet of scalding steam.

 

[pmx_super]

WHat volume of water is in the heater?
On vessels up to 15litres I've only seen pressure relief valves, not temp and pressure ones which are required on larger vessels, but you need to check with the manufacturer.
The discharge has to go outside, safely but visibly. It could be a dribble, but it could be a jet of scalding steam.

It's 7 litres. The manufacturer provides the appropriate valve.

Would it be possible to discharge into the waste pipe from the sink?

Oh, and what might happen if I omitted it all together? Wouldn't it just blow steam back into the cold water inlet / out of the hot tap, or might the whole unit explode!?

 

[ChrisR]

Most of these heaters aren't plumbed in 100% properly. Usually they should have pressure reducing valve, isolating valve, check (one way) valve, expansion vessel and pressure relief valve.

Without knowing the details we have to say yes, it could explode.
The discharge needs to be visible.

 

[pmx_super]

Thanks for the i/p.

You're right btw - it's just a pressure relief valve that's required as standard.

 

[chrishutt]

.....Oh, and what might happen if I omitted it all together? Wouldn't it just blow steam back into the cold water inlet / out of the hot tap, or might the whole unit explode!?

http://www.waterheaterblast.com/

 

[pmx_super]

wow. I'm sold.