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PulsaCoil
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Replacing a Pulsacoil

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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 water cylinder.

The Gledhill PulsaCoil IIIs, PulsaCoil 2000s and Pulsacoil A-Classes transfer heat into the tap water using a pump and an external 'plate heat exchanger'. A plate heat exchanger is a block of very thin stainless steel plates arranged so that cold mains water can flow through one set of spaces between the plates, and hot water from the thermal store core can flow through an alternate spaces. Heat transfers through the plates and heats the cold mains water on it's way to the hot tap.

How does the PulsaCoil BP work?

An immersion heater heats the low pressure water inside the thermal store. High pressure cold mains water flows to the hot taps via a long coil of copper tube fitted inside the thermal store and immersed in the hot store water. Heat from the store water heats the cold mains water as it passes through the coil on it's way to the hot tap. The output temperature to the hot taps is prevented from being dangerously hot by a thermostatic blender valve on the outlet of the domestic heat exchanger which adds in some cold water if necessary. The blender valve output temperature can adjusted by the user.  

 

PulsaCoil BP faults:

1) Depleted water in the thermal store. 

PulsaCoil BPs have a top-up cistern attached to the top. 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.) Water is continually lost from the thermal store through evaporation and/or leaks, and when there is no float valve to top it up, the user needs to do it manually from time to time. Low water level in the cistern at the top will eventually prevent a PulsaCoil BP from working properly  because once the top-up tank is depleted, the water level inside the store begins to fall too. Once the heat exchanger coil is no longer fully immersed in the thermal store water, hot water performance will be affected. 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.

The 'Skel' brand immersion heaters (fitted as original equipment) seem to suffer from leaks in the thermostat sensor pocket as they grow old. 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) Thermostatic blender valve failure.

The thermostatic blender valve is susceptible to contamination by water scale in hard water areas. There is a component inside which breaks and the blender valve delivers just luke-warm water to the taps. A new blender valve cures the problem.

 

5) Water scale-contaminated internal heat exchanger coil.

The plate heat exchanger is prone in some areas 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 too. The fix is to either fit a new plate heat exchanger, or to descale the existing heat exchanger using conventional descaling techniques. 

6) 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 is difficult. I keep them in stock myself as a result. 

 

If you'd rather I came and fixed your PulsaCoil BP, contact me here

 

 

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First published 12th January 2013
Last updated 12th January 2013

Copyright 2013 Michael Bryant