Immersion Heater heating top of tank - but no hot water

Rosarius · 12 Apr 2007

In the absence of a CH boiler right now, I'm depending on an immersion heater to heat the hot water in the cylinder. The immersion is working but I'm getting no hot water. The immersion is situated on the top of the tank, down vertically into the tank.

There is a hot water vent pipe right out of the top of the tank that returns to the the cistern above, and the first few inches of this are hot. The hot water feed to the hot water pump comes off the tank about 85% up the side but never seems to draw hot water. At the weekend, before my central heating boiler gave out, hot water was fine.

What might cause this? The stat on the immersion is set to 65 degrees.

breezer · 12 Apr 2007

my thoughts

water comes out of the cylinder (heated by immersion heater or bolier) under the pressure of water from the header tank.

the hot water comes from the top, and the cold water goes in at the bottom

so you have a blocked pipe? or the header tank is empty

(header tank will be above the cylinder , so probably in the loft)

JohnD · 12 Apr 2007

you are talking about hot water to the taps?

do any of the taps have hot water?

Rosarius · 12 Apr 2007

No. None of the taps has hot water.

I've even run the shower at full blast on hot (although cold) to empty out the tank and force it to refill. As I said, when the hot water was heated by the boiler downstairs, hot water was fine. Just the immersion doesn't seem to do the job.

nickso · 12 Apr 2007

wait im confused

....doesnt take much i know

are you saying you have no water coming out of the taps at all or water is coming out but its stone cold?

gas4you · 12 Apr 2007

How have you checked that the immersion is actually working?

Rosarius · 12 Apr 2007

Water is coming out of the taps. The pump whcih engages when the hot taps are turned on is working. But the water is stone cold.

I presume the immersion is working because, once turned on, there is heat in the vent pipe at the top of the tank.

JohnD · 12 Apr 2007

I understand you to say that the hot water is not drawn from the top of the cylinder, but part way down. This is unusual, unles there are some "priority" taps fed from the top of the cylinder.

Possibly the immersion heater is not warming much of the cylinder, just the top part.

This might be because it is a very short immersion heater, or because the thermostat is set too low and it cuts out quickly.

The pipe at the top of the cylinder ought to be too hot to comfortably keep your hand against.

Do you feel able to isolate the power to the immersion heater and carry out some tests? You will need a multimeter and screwdrivers.

nickso · 12 Apr 2007

hmm

if i were there myself i would be checking the immersion is working as far as possible by checking it has 240v on both sides of the stat. it may have tripped out. of course you say there is heat....so......

have you had to use the immersion before? did it work then?

is there a chance that its too short for the cylinder its installed in?

gas4you · 12 Apr 2007

How about the possibility that op has only got an 11" immersion fitted by 'mistake' in large cylinder so the draw off at 85% height is not in the hot water area???

gas4you · 12 Apr 2007

Think we crossed nickso without knowing it

nickso · 12 Apr 2007

john beat me by a second or two

Rosarius · 12 Apr 2007

I've never had to depend on the immersion before. It could be too short for the tank.

The hot water feed comes out of the tank about 40cm from the top. the only pipe directly out of the top is the vent. Although it appears that this may once have been the hot water pipe before the pump was installed - it does have one capped off end.

I've just turned the stat up to 80 to see if that makes a difference.

Rosarius · 12 Apr 2007

JohnD - there is voltage across the terminals of the heater, but with the stat at 60, the tap at the top was very warm, but not uncomfortable to the touch.

JohnD · 12 Apr 2007

does this voltage come and go as you adjust the thermostat?

If so, undo and pull out the thermostat (no water will come out, it is a rod sliding down a sealed tube inside the cylinder).

See how long it is.

What are the dimensions of the cylinder?

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Immersion Heater heating top of tank - but no hot water

breezer

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