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 water cylinder.

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.

Common problems:

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 approximately.

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. 

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This page last edited 4th June 2008