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Andrew Smith
Andrew Smith, Plumber
Category: Plumbing
Satisfied Customers: 3629
Experience:  City and Guilds qualified plumber
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my hot water cylinder only gives hot water for a little while

Customer Question

my hot water cylinder only gives hot water for a little while and then the water goes cold.I have had both the elements changed but without any joy.The water goes cold halfway thru a shower.I think it is an "unvented direct system" but there are no labels on the cylinder to say exactly which system it is.-It looks very much like a megaflow system as illustrated on the plumbase site.I have turned up the thermostats (on the elements) to no avail.
Any suggestions as to what could be wrong?
Submitted: 4 years ago.
Category: Plumbing
Expert:  Andrew Smith replied 4 years ago.

Plumbers_Mate : Is it just heated electrically?
Customer :

Yes. It is in a two bed flat.The heating is by way of electric radiators and hot water is this immersion heater --and it is not on a cheap night rate or anything like that--just straight on/off switch

Expert:  Andrew Smith replied 4 years ago.
If this is only the way to heat your hot water then there is usually a timer involved.
Is there not one in the airing cupboard or in the kitchen?
Customer: replied 4 years ago.

N o there is no timer anywhere

Expert:  Andrew Smith replied 4 years ago.
Do you have 2 consumer units or one that is split down the middle?
Customer: replied 4 years ago.

What do you mean by consumer units? There is a switch (on/off)next to which is another ---up-sink only,down-bath. I have tried both combinations over the past 3 days.

Customer: replied 4 years ago.

Will you replying anytime soon?????????????

Expert:  Andrew Smith replied 4 years ago.
I am only on here when not at work.
Your main consumer unit (fuse box) sometimes when you have electric heating there are periods during the day when they come on and also at night, not like standard economy 7.
How long have you had this problem?
Customer: replied 4 years ago.

The fuse box has about 10 fuses all in line,and one of them says "hot water".The fuses are all fine.and there is power right up to the element. I have had this problem only the last six days.


I have been fiddling with it and last night I pulled out the sensor/thermostat --which is like a copper pencil at the end of a coil--and that was embedded in a hole in the cylinder.It is now just hanging outside. But I now have a lot more (quantity)hot water than in the last six days. But there is still not enough for a reasonably long shower. Do you think changing this sensor will cure the problem?

Expert:  Andrew Smith replied 4 years ago.
The immersion heater you have has a long and a short element (bath or basin).
The short one will only heat the top 1/4 of the cylinder nod the long one will heat the top 2/3.
Your long element is broken.
You will need to replace your immersion heater.

DO NOT USE YOUR IMMERSION HEATER WITH THE THERMOSTAT OUT OF THE POCKET, your water could boil and you can burn yourself.
Customer: replied 4 years ago.

Thank you for the answer. I saw the plumber change BOTH the elements.


They were both the same size !!!And the old ones he took out were both similar.


The thermostat out of the pocket--would not the elements' thermostats cut in and stop the water getting hotter than the 55* they are set at?

Expert:  Andrew Smith replied 4 years ago.
The thermostats sit in the pockets, the water has to be turned off and the immersion heater remove for them to swap it?