PART P - NICEIC

TECHNICAL IMMERSIONHEATERS
IMMERSION HEAT E R S
The importance of thermostats and the possible hazards associated with hot water
systems are well understood; manufacturers of domestic water heating products must
incorporate safety devices and thermostats to protect the people who use them. However,
thermostat failure can occur with immersion heaters, particularly towards the end of their
working life.
According to AMDEA, the Association of Manufacturers of
Domestic Appliances, there are about 16 million household
immersion heaters in operation in the UK, of which about one
million are replaced annually. A small proportion of these
immersion heaters fail due to the thermostat contacts failing
closed, causing the water in the storage cylinder to boil.
Up to the end of March this year, there were two product
standards for household immersion heaters in effect. However,
BS 3456 Part 2 Section 2-21 was withdrawn on 1 April. From
that date, BS EN 60335-2-73: 1997 – Safety of household and
similar electrical appliances – Part 2: Particular requirements –
Section 2.73. Fixed immersion heaters became the only
applicable standard for household immersion heaters. This means
that all new household immersion heaters manufactured for sale
should now comply with this standard.
BS EN 60335-2-73: 1997 brings household immersion heaters
for vented water systems into line with existing requirements for
unvented water heaters and other domestic applications.
The 1997 standard recommends all fixed immersion heaters
installed in a water tank in a vented system in a household, or
used for similar purposes, incorporate a safety cut-out
independent of the immersion heater tank thermostat, to limit the
temperature of the stored water should the thermostat fail.
The cut-out should not reset automatically, and the water
temperature should not be permitted to exceed 98 °C.
The requirement for a safety cut-out independent of the
immersion heater tank thermostat may be satisfied by either:
• a single operation device that cuts out when the water
exceeds the safety limit (such a device would then need to be
replaced after it has operated), or
• a device that can be reset manually after it has cut out when
the water exceeds the safety limit.
The safety cut-out devices may be either:
• separated completely from the thermostat, or
• combined within a separate section of the thermostat.
In summary, any fixed immersion heater that is repaired, replaced
or installed in a tank in a vented water system in a household (or
used for similar purposes) should now be manufactured to
BS EN 60335-2-73: 1997, to comply with current European and
national safety legislation.
However, contractors and others may still be holding some stocks
of the old immersion heaters. The changes introduced in the
1997 European Standard have improved the product, but this
does not imply that products conforming to the previous British
Standard were unsafe.
AUTUMN
20 04
 
 
 
 
 
 
 
 
 
 
 
 
 
 NICEIC CO N N EC T I O N S 3
2