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 How to descale your home electric water boiler / heater


Time after time scale deposit built-up in your electrical home hot water boiler. Consequence is an increase of electrical consumption due to the fact that scale prevent correct heat exchange and also a diminution of the boiler capacity due to the volume of the deposit. 

After few year of use descaling needs to be performed. Time interval will depend especially of the water hardness of your location. But it may be done each 2 or 3 years interval.

Obviouly you can try to use a chemical descaler but you will not be sure to have removed all the scale. Taking into accont quantity than can accumulate a lot of product will be needed. Then as such types of products are based on acids they are not really environmental friendly. Proposed method is to open the water heater for scale removal.

This operation is quite simple but requires some knowledge in electricity and plumbing.

The pictures are taken on horizontal water boiler but process and architecture is identical on vertical ones.

First operation is to cut electrical current of boiler with the circuit breaker. If you are not sure, cut the whole installation and/or check with a voltmeter.
Then cut the main water supply of the house.
Do not continue if these two operations are not made they are crucial for safety.

Note: you can stop electrical power one day before this will avoid to waist hot water and will lower the temperature inside for further operation.

Next open a tap to decrease water pressure (open hot and cold). When not more water comes out from tap, Then you can activate the safety group (little tap fixed on the boiler cold water pipe). Such operation may take some times as you need to drain completely the boiler. As an alternative you can disconnect inlet pipe to drain but you must anticipate how to evacuate water. Take care that water inside can be very hot.

When you are sure that boiler is empty :
- remove plastic cover that protect electrical parts and resistor, this is also the way to open the boiler.

- Disconnect electrical connection, draw a scheme or take a picture for reinstallation.

- Now remove nuts that maintain resistor element plate. This plate maintain resistors and plugs inside of the boiler.

- Carefully remove resistor plate, take care not to damage seal. If boiler is really scaled it could be difficult to extract resistor.

- You have now access to inside of your boiler. You should see heavy deposit of scale on resistors and in the tank. On vertical boilers major part of scale may exit alone. On horizontal ones scale will remain inside.

- Wash inside of the tank, you can use water vaccum cleaner and/or brush.

- Carefully clean resistors (or resistor tubes for steatite boiler type) with a metallic brush. Take care not to damage resistor surface.
- Check condition of resistor and anode. Anode may show some trace of corrosion (wear) but has to be strong enough to ensure protection of tank from corrosion.

- You can now reinstall parts. It is recommended to replace the plate seal to ensure correct sealing but if old one is in good condition it could be reused. 
- Put back the resistor plate and tighten the nuts. Process with one nut and then the opposite etc...
- Plug electrical connection and check water pipes. Also check that safety group is in good condition (button can be easily moved and it doesn't leak, if not replace it by a new one.

- Now you can re-open water supply and check that there is no leakage for the plate seal. Reinstall plastic cover and reconnect circuit breaker.