The Immersion Heater

(This may be your way out of a crisis)

 

This article is for people with a hot water storage cylinder. If you’re lucky enough to have a working immersion heater, then if (or more accurately when) your boiler isn’t working, you can still have hot water heated by electricity- great in an emergency.

 

Because boilers work nearly all the time, for years on end, many people know little about immersion heaters or even if they have one, and if this applies to you, you may benefit from reading on.

 

If your boiler is a combi, which heats water instantaneously on its way to the taps or shower, and you have no hot water storage, then this isn’t for you. If your boiler breaks down and you don’t have an alternative source of hot water, such as an electric shower, then you’ll have no hot water until it’s fixed.

 

If you know about immersion heaters, know where yours is and that it works, you probably won’t want to read the whole article, but here are a few tips:

  • Some people turn off the boiler in the summer and use the immersion heater to provide hot water. Be aware that per unit of energy, the cost of electricity is about four times that of gas. Even allowing for the fact that not all energy used by a gas boiler heats the water, electricity is an expensive means of heating water. Furthermore, failure to exercise items with moving parts such as pumps and motorised valves may cause them to seize up and cause your system to fail at the start of the heating season (and that’s when most failures do occur).
  • Immersion heaters run at 3 kilowatts. A typical gas boiler produces between 12 and 24kW on full power, so will heat water four to eight times faster. Once you’ve used a sizeable quantity of hot water, for a bath or shower, the immersion heater has a long “recovery time”.
  • Immersion heaters come with a (replaceable) thermostat and will turn off when the cylinder water reaches temperature. Because of this and the long recovery time, leave it on.

 

Because boilers work nearly all the time, for years on end, many people don’t know about immersion heaters, and if this applies to you, there’s no need to feel embarrassed, but you may benefit from reading on.

 

How to spot an immersion heater:

If you have a traditional copper cylinder, the immersion heater, if present, will be fitted in the top and look like this:

 

Note the cable emerging from it: it’s not that uncommon to find an immersion heater fitted but not connected. If so, it will need to be connected by an electrician so it can be used when the emergency happens. The good news is that it will almost certainly be in pristine condition.

 

If you see this, it’s a blanking plug, and bad luck, you don’t have an immersion heater:

It’s been hacked about in an unsuccessful attempt to remove it.

If you have an unvented cylinder (often known by the Heatrae Sadia trade name of “Megaflo”), it will be fitted in the side, and may look like one of these: the immersion heaters and thermostats are behind the grey covers and the cylinder on the left has two heaters:

How to check it (non-invasive method):

The simplest way to check if the immersion heater works is to switch it on or plug it in, providing the cylinder isn’t full of hot water, which may cause the thermostat to switch off. When the immersion heater is operating, there is often a slight fizzing sound from the cylinder, or a faint buzz – you may well need to put your ear against the cylinder to hear it.

 

If it appears not to work, check your electrical consumer unit and ensure that the circuit breaker for the heater is switched on, or for older installations, the fuse is fitted and intact. There may be a fused switch near the immersion heater – check the fuse is intact (it should be 13 amp – the heater runs at about 12 amp [I have found a blown 3 amp fuse]) and the switch is on. Check if there’s a timer that’s currently off.

Accessing the immersion heater:

Before attempting to access the immersion heater:

  1. Isolate the immersion heater electrically by switching it off, turning off the circuit breaker at the consumer unit, or unplugging it. Preferably, do more than one of these if you can.
  2. Check it really is isolated, because with the cover removed, it will be easy to touch exposed parts that are live when the immersion heater is on. There is a lot of earthed metal in the form of the cylinder and pipework – it would be easy to get a fatal shock.

 

Remove the cover:

The following image shows an immersion heater for a vented copper cylinder, including the part we don’t normally see. The cover is secured using a single nut – very common. Details may differ, but a single fixing of some sort is the norm.

(The heating element is the pair of bent tubes – the straight rod is the thermostat.)

 

Once the cover is off, here’s what will be revealed, though details will differ. You may well not see it in all its glory because:

  • The immersion heater may be tilted away from you.
  • The cupboard will be dark.
  • There will probably be a shelf that prevents you getting your head in for a look.

 

Once the cover is off, here’s what will be revealed, though details will differ. You may well not see it in all its glory because:

  • The immersion heater may be tilted away from you.
  • The cupboard will be dark.
  • There will probably be a shelf that prevents you getting your head in for a look.

 

If all else fails, the thermostat can be replaced – they are not expensive. It is removed by undoing the two screw connections and pulling out the connecting wires. The thermostat can then be pulled out. Ideally it should be replaced by one of similar length, but a shorter one may suffice to get things going. The aim is to achieve a water temperature of 60 celsius or more to kill any Legionella bacteria that might be lurking, so if the thermostat is marked with the temperature, set it to 60.

 

If this article has helped you end up with a working immersion heater, then excellent. Let’s hope your hot water crisis if you have one, is over soon, and you can forget about it until the next one!