Hot water tank working...but not coming through

[Masos]

Whilst we wait for an oil delivery we've had to turn our central heating / on demand hot water boiler off. Luckily, we still have the old hot water tank (electric immersion heater) which I turned on this morning. The challenge is that I know it's heating the water, but I can't get any more than a cup-full of water if that, to come through.

Here's what I've done:

1. connected the power to the tank and turned it on (I can hear it 'humming' when turned on)
2. opened the valve on top of the tank to allow hot water to be supplied

When I turn on a hot tap, for a split second or two I get hot water, but then it goes back to cold.

I am wondering if the little black 'tap' in the attached image may hold the clue. It seems to be stuck in the upright position and doesn't want to move even with some WD40 applied. Could this be stopping the supply of new water getting to the tank, and hence stopping all pressure in the system, thereby stopping me getting hot water?

Untitled

• Masos
• 9 Mar 2011
• 1

When I open the red overflow valve also shown in the image, hot water does flow out of the tank.

Can anyone shed any light on the black tap in the image? What is it for and could it be the cause of my problems?

Appreciate any advice or ideas people have.

Thanks.

 

[electronicsuk]

You say your oil boiler provides on demand hot water, so presumably it's a combi. If that's the case, I can't see how you can be running what appears to be an unvented cylinder side-by-side with a combi, unless each system feeds a separate set of outlets. Care to elaborate?

If the cylinder in your picture previously had the supply isolated, perhaps it isn't intended to be used any more, or if it is, there may well be a set procedure to isolate the DHW supply from the boiler BEFORE filling the cylinder.

I suspect that the cylinder outlet and combi DHW outlet may simply be teed together, in which case this could prove very dangerous by allowing mains pressure water into the outlet of the unvented cylinder, completely bypassing the pressure reducing valve!

 

[Masos]

The central heating system is a Viessemann oil boiler with a very small seperate water cylinder. It's located about 10 metres from the original immersion heater, in a room accessed from outside the main buiding and does indeed feed different outlets to the unvented cylinder (all cylinders in France are unvented).

It is intended for use as a fallback option, and was something the previous owner took me through nie on 4 years ago when we took possession. We've had cause to use it once before, and ...well, I'm a little rusty I guess.

Do you have any ideas on y original question regarding the purpose of the little bliack tap indicated in the image?

Thanks

 

[picasso]

The little black tap looks like the main valve to the cylinder, if its plastic take it off and use spanner directly on to the tap head, gently otherwise you will have an unscheduled discharge of water aka a leak.

 

[Masos]

Thanks for that - should it just ping off with a screwdriver?

 

[picasso]

hard to tell from the photo, try it and see.

 

[Masos]

You're a star - it did ping off incredibly easily and al became obvious. We now have hot water!

Thanks again.