What IS a PulsaCoil?
PulsaCoils are thermal stores, rather than hot water cylinders. Like
conventional hot water cylinders, a thermal store is a container filled
with hot water but here the similarity ends. Once filled, the water in a
thermal store never changes. Instead, the heat stored in it is used to
heat the tap water using a heat exchanger. This allows the hot tap water
to be delivered at full mains pressure, and is one of the primary
benefits of installing a thermal store instead of a conventional hot
How does the original PulsaCoil work?
An immersion heater heats the water inside the thermal store. The Gledhill PulsaCoil transfers heat into the
hot tap water by passing the cold mains water through a coil of pipe
inside the unit, immersed in the store of hot water. Heat passes through
the wall of the tube and heats the cold mains water on it's
way to the hot tap. To prevent the temperature of the domestic tap water
being too high, a thermostatic blender valve mixes in a proportion of
cold water. The output temperature can be set by the user.
The majority of PulsaCoil problems fall into one of the following categories:
1) Depleted water in the thermal store.
Original PulsaCoils have a top-up cistern built into the top of them. This
may or may not have a float valve connected to the mains water supply to
fill it. When there is NO mains connection, there is usually provision
for manual filling by the user by means of a tap on the wall nearby.
When the user doesn't realise this, water lost from the thermal store through
evaporation and/or leaks can prevent the PulsaCoil from working. If the water
level falls too low, the heat exchanger coil ceases to be immersed in
stored hot water so when a hot tap is turned
on, and the unit will not deliver hot water. The problem is progressive.
As the water level reduces, so does the hot water performance. The answer is to check the
water level in the top-up cistern and top it up to the waterline
embossed into the wall of the cistern.
2) Immersion heater element failure.
The unit fails to heat up. Easily diagnosed by measuring the
resistance of the heater element. A good element will measure 18 Ohms
3) Immersion heater leaking.
Older 'Skel' brand immersion heaters (fitted as original equipment)
seem to suffer from leaks in the thermostat sensor pocket. On many
occasions I've seen water emerging from the copper tube in which the
thermostat sensor is housed. This is clearly dangerous as it introduces
water into the electrical connection box on the heater element head, and
it often results in thermostat failure. The only repair is to replace
the whole immersion heater and thermostat.
4) External Economy Seven time clock failure.
PulsaCoils are usually connected to an Economy Seven tariff
electricity supply. When there is no separate off-peak power supply to
the unit an Economy Seven timer will have been fitted. These seem to
fail after a few years and no longer deliver power to the immersion
heaters, even when the indictor lights on the timer say power is being
delivered!. Although it's a straightforward matter to replace these
timers, finding an electrical merchant who keeps them in stock can be
very difficult. I keep them in stock myself as a result.
4) Water scale-contamination of the coiled-pipe heat exchanger.
The coiled-pipe heat exchanger is extremely prone to water scaling.
This presents as maximum water temperature becoming progressively lower,
and in the final stages of scaling, the flow rate from the taps reducing
to almost zero. Chemical descaling is the only answer, using
conventional descaling chemicals and techniques.
If you'd rather I came and fixed your PulsaCoil, contact me here
First published 2nd January 2007
Last updated 12th January 2013
Copyright 2013 Michael Bryant