Electric Hot Water Heater

[Donquick]

Hi all,

Can i just ask for clarification on something please. I am installing an electric hot water heater in a flat. It is in a closed, unvented circuit. There is no boiler or anything else, just cold mains to all taps in the flat and a simple hot circuit fed direct from the water heater. Just so you know it is in Spain so some of the plumbing fittings etc are different from ours as shown in the photos below.

The tank is 80 litres and horizontally mounted with two brass threaded connections along the bottom horizontal edge marked blue and red. The instructions (not shown as i have left it in the flat javascript:emoticon('') ) show the hot connection simply connected to the hot outlet onto the hot pipe to feed that circuit. The cold is shown as a T off of the cold circuit, then a stop valve, then a pressure reducer (if req. for > 5 bar) , then a pressure relief device, then the tank connection. In my opinion it is a bit ambiguous as the drawing is a bit random.

The tank comes with the pressure relief device shown in the photo. It is the thing on the right. I am happy to go with what is shown on the diagram but i just wanted to check first. Putting this in the cold feed to the heater just goes against the grain. For a start it has got a red plastic lever which screams hot to me and my natural tendency is that it is the hot outlet that needs the expansion/relief valve not the cold inlet. Surely, the pressure in the cold inlet as the water expands on heating is irrelevant. My second question is whether anybody has seen a pressure relief valve like this before, it has a very small outlet (for the vented pressurised water) about 6mm across. Anybody had any experience of getting this to thee right size to input into the drain?

Here is the photo of the pressure relief valve and a shot froom the picture on the box which might help:

Untitled

• Donquick
• 8 Dec 2014
• 1

Untitled

• Donquick
• 8 Dec 2014
• 1

Thanks for your help.

Don

 

[OwainDIYer]

I think in the UK there is a pressure relief on the cold side, and a temperature+pressure relief on the hot side. Often the cold pressure relief is combined with a pressure reducing/balancing valve which may have a tee-off for balanced cold pressure for mixer showers etc.

 

[Donquick]

Thanks for the quick answer. I see what you mean, but that has made me even more unsure . I guess the question is this. Presuming that I can get away with using what was provided in the box, does it go in the cold inlet or should it go on the hot outlet. Looking at the picture from the box, it suggests that the hot water is propeled from the cylinder at the top by the incoming cold pressure and expansion could be taken care of on the cold branch as long as there was a non return valve before it.

Anybody?

 

[OwainDIYer]

Presuming that I can get away with using what was provided in the box

I'm not sure you can.

The thing with the red lever might only be a drain tap? or for venting air to prevent an air lock in the cylinder? It might not be a pressure/temp relief valve at all?

In the UK an unvented cylinder would come with comprehensive instructions and (legally) only be fitted by someone with an unvented hot water qualification.

 

[Donquick]

Thanks - I will ask a plumber here. I think that my device is a relief valve as it I have just had a look at some videos on youtube and it is exactly the same as all of the temp / pressure relief valves used as standard on the American electric water heaters. Anyway, thanks for your help, I will ask here for some pro advice as you recommend.