1) Economy Seven Electricity Tariff:
2) The maintenance task they can do to avoid the occasional unnecessary repair engineer visit.
3)The weird behaviour of the hot water when a tap is first turned on
Economy Seven Electricity Tariff:
Understanding the concept of 'cheap rate' electricity is central to running a PulsaCoil economically. Due to the way electricity is generated, there is surplus capacity during the night and this is sold at a far cheaper rate than daytime electricity. You need to make sure you are on the right billing tariff and have a dual-rate (Economy Seven) electricity meter installed.
The most common cheap-rate (or night-rate) tariff is called "Economy Seven", but there are many others according to which you electricity supplier you have. Electricity burned during midnight and 7.00am is typically charged at about one third of the price of daytime electricity. PulsaCoils are designed to take advantage of this price difference, and should be wired up so the lower immersion heater (which heats the whole of the tank by virtue of being fitted at the bottom - heat rises), is only powered during the night. The upper immersion heater, which only heats the top one-third of the store, is connected to the daytime (expensive) supply and is intended only to be turned on in two circumstances. Firstly, temporarily by the user on the odd occasion that the hot water runs out before the next automatic night-time re-heat. or secondly, as a back-up should the main Economy Seven heater element in the bottom of the tank fail.
Unfortunately, many users leave both immersion heaters turned on permanently. This results in unnecessarily high day-rate (expensive) electricity consumption, and worse, it masks failure of one or other immersion heater as the other heater continues to provide hot water. The first heater element failure only becomes apparent when the second one fails too, and then there is NO backup element available to provide emergency hot water. The back-up element is not intended by the designers to be left turned on all the time for these reasons.
A maintenance task the the user can do to avoid the occasional unnecessary repair engineer visit:
All PulsaCoils have a top-up tank to keep the unit heat store full of water. Small amounts are continuously lost by evaporation and minor leaks, and top-up tanks are conventionally connected to the mains supply with a float valve, but due to difficulties installing overflow pipes, many builders of luxury flats do not do this. The end result is that the water in the heat store gradually reduces over a period of years. Eventually the system stops working and the only action the repair engineer takes to fix it is to top up the water with a bucket - something the user could have done if they realised!
PulsaCoil 2000s have a separate black or grey plastic tank fitted above them with a lid on it. Lift the lid off and top it up once a year to about half-full. Sometimes there will be a water connection with a valve the user can manually turn on then off again to do this. Other times a bucket will be needed.
All older PulsaCoils have a circular grey metal top-up tank incorporated on top of the unit. There is a tightly fitted white plastic cover about seven inches in diameter that has to be removed to check/top up the level. Again, the tank needs to be about half-full or more, and there is a groove embossed around the tank as a waterline. PulsaCoil IIIs have a float switch that shuts the unit down when the water level falls too low.
The weird behaviour of the hot water when a tap is first turned on:
This applies to the PulsaCoil III, PulsaCoil 2000 and the PulsaCoil A-Class. The PulsaCoil and PulsaCoil BP behave 'normally'.
When a hot tap is turned on, hot water is delivered because the heat exchanger is hot, but the pump in the unit only starts running when the heat exchanger cools significantly. This means there is a big fall in water temperature about 30 seconds after hot water arrives at the hot tap, and then it recovers. This is normal behaviour. When a hot tap is turned on, firstly cold water comes out, then the water warms up, then it cools again (as the heat sensor tells the pump to start), then the hot water returns and the temperature becomes stable.
Many users notice this initial unstable temperature and (incorrectly) think their unit is on the brink of going wrong.
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Copyright Michael Bryant 2020
Site first published 2nd January 2007
Last updated 21st March 2020
Gas Safe Register 197499, CIPHE registration number 56207