Immersion heaters are used on hot water storage cylinders to heat up the stored water. The temperature is controlled by a thermostat which swiches off the immersion heater when desired temperature is reached. Current regulations state that all thermostats fitted after April 2004, should incorporate a over temperature safety cut out device. Essentially this means if a fault occurs with the thermostat, the safety cut out device will disable the immersion heater to prevent the water boiling.
In a recent article (Jan 2008) published by the Water Regulations Advisory Scheme (WRAS), attention was drawn to the potential dangers of immersion heaters. The following We have included extracts of this document belowthe following
INTRODUCTION
Householders may have seen recent press reports of a risk of
scalding arising from the collapse of plastic water
storage cisterns containing very hot water due to electric immersion
water heaters which fail to switch
themselves off. The background to the incidents which have been
reported is outlined below for information.
Serious incidents of this type are very rare, but two fatalities
in four years from the same cause make it prudent
to carryout checks of older plumbing systems where this equipment
may be installed.
The following advice is to re-assure householders and landlords
regarding the likely risks and to advise them
about relevant checks of their plumbing systems and what to do
if they are planning to change their storage
cisterns or immersion heaters.
WHAT CAUSED THE FATAL SCALDING?
The recently reported incident occurred in a house, where a faulty
electric immersion heater which heated the
domestic hot water failed to switch off when the normal hot water
temperature was reached (electrical
thermostat failure). This caused the water in the hot water storage
cylinder to boil. To avoid overpressurisation
of the hot water cylinder, the plumbing system operated as designed
by allowing the boiling
water to discharge through a vent pipe into a plastic storage
cistern (tank) in the roof space. This continued for
some hours until the plastic tank was full of very hot water,
and partly because it wasn’t properly supported
underneath, it distorted and split, spilling the very hot water
onto the bedroom ceiling above a child's cot. The
hot water cascaded onto the baby sleeping in the cot, who suffered
severe scalding from which she
subsequently died.
CURRENT REQUIREMENTS
Not all water heating systems use immersion heaters. If you are
replacing an existing immersion heater or
storage cistern or having a new installation, insist on the equipment
and installation meeting the following
requirements.
Electric immersion heaters made in accordance with British Standard
BS EN 60335-2-73:20031 include an
independent non self-resetting over-temperature cut-out safety
device to prevent water in the hot water cylinder
from overheating. This is in addition to the normal switching
mechanism of the immersion heater.
Since April 2004 it has been recommended that any repair, replacement
or installation work on domestic
immersion heaters should include the fitting of such a safety
feature.
Recently-built houses and flats may not have water storage cisterns
at all, instead having all their water supplied
directly from the water main. Where water storage cisterns are
used they are often located in the roof space
above the upper rooms and are typically used to store cold water
for use directly, for example at bathroom taps,
and to supply water to the vented hot water system.
Modern plastic cisterns should be able to contain boiling water
without collapsing or splitting, provided they are
adequately supported.
SIGNS OF A PROBLEM WITH YOUR IMMERSION HEATER
There are a number of warning signs if the immersion heater is overheating the
hot water:
(a) Excessively hot water coming out of the hot taps;
(b) Excessive noise or ‘bubbling’ from the hot water cylinder
(c) Hot water coming out of certain cold water taps. (Some storage cisterns also
feed cold water taps,
for example in the bathroom).
(d) Steam or condensation in the roof space.
(e) Unusual warmth between the insulating cover and cistern (tank) sides on the
outside of the cold
water storage cistern in the roof space (that is, more warmth than would be due
to the surrounding
air temperature).
If you suspect there is a problem with the immersion heater, arrange for a qualified
person (plumber or
electrician) to check it urgently. If you are a tenant, depending on the terms
of your tenancy, arranging and
paying for these checks may be the responsibility of your landlord. If so, ask
the landlord to arrange the checks
as a matter of urgency.