A New Standard
for Fixed Immersion Heaters
British Standards Institute.
The new European Standard, EN60335-2-73, replaces the old BS3456 Part 2 and introduces new requirements of construction and, for the first time, stipulates a maximum water temperature for installations using a fixed immersion heater.
The most significant clauses of the new Standard are 19 and 22 and any person or organisation that repairs, replaces or installs immersion heaters should be aware of them.
OPERATION, requires that the
immersion heater is able to withstand an input of 15% over the rated power input
and during this test, the water temperature in the cylinder must not exceed 98°c.
requires that any over
temperature protection device that is used in compliance with clause 19 must be
simply means that the cut-out must remain open circuit until it is manually
further requirement of clause 22 is that the sensing device and cut-out contacts
should operate independently of the thermostat or temperature control.
There are an estimated 16 million immersion heaters in operation in the UK and 1 million are replaced annually, and of these some 10,000 fail with the thermostat contacts closed.
The consequences can be disastrous, and in many cases these incidents can result in damage to property and occasionally cause injury to persons.
The old standard applying to fixed immersion heaters had not been reviewed for nearly thirty years and the European Standards Authorities have been concerned for some time that the risks associated with these runaway immersion heaters are too great.
British Standards Institute has allowed a transition period during which
immersion heaters and thermostats to the old Standard may be sold alongside
those complying with the new, but that does not eliminate the duty of the
installer to offer the client the best possible advice.
All organisations dealing directly or indirectly with the public are required, by law, to exercise a ‘duty of care’, and that liability now extends to the directors and officers of the organisation, personally.
now a conventional defence to ‘duty of care’ was that the technology
available at the time of sale was not sufficiently advanced to enable an
alternative, safer product to be offered. This
defence will no longer work in the event of an injury resulting from a failed
immersion heater and thermostat, as
safety thermostats incorporating an over temperature cut-out are now
thermostats incorporate a temperature control plus an over temperature device
and prevent water in the system from boiling.
There are no excuses for not upgrading an old installation to comply with
the clause 19 and 22 requirements as most safety thermostats
are suitable for
direct replacement of the old rod thermostats.
are currently two types of safety thermostat available:
shot devices which will cut out once when the water temperature
exceeds the set safety limit and then have to be replaced.
They are susceptible to cut out caused by external heat sources such as a
central heating boiler and should therefore be avoided in all but the simplest
immersion heater applications.
for most applications is the type which incorporates a cut-out
that can be reset and re-used, which are generally a fit and forget device.