Step-by-Step: How to Drain a Worcester Bosch Combi Boiler

Why Do I Need to Drain My Boiler?

Overtime, sludge (mineral and oil deposits) can build up inside your boiler unit, causing it to become less efficient as it has to work a lot harder to heat the water passing through. By draining your boiler of this sludge, you can minimise this build up and keep your unit running cost-effectively. Plus, draining your boiler regularly should extend its lifespan and will mean you can postpone having to pay for repairs and replacements.

You may also need to drain your boiler if you are redecorating or removing your radiators from walls for another purpose such as changing your pipework. It can also be helpful to drain your boiler if you are going on a long-haul winter holiday – this is to reduce the risk of pipes freezing over.

Checking for Sludge

How do you know whether or not sludge is building up in your boiler unit? This is easy: simply release the air from one of your radiators and check the colour of the water. If the water is clear, there is no sludge, but if it is dark in colour it is recommended that you drain your boiler.

How to Drain a Worcester Bosch Combi Boiler: 5 Steps

Draining your boiler is a simple process, and all you will need is a few hours and a hose. Here are 5 quick steps to follow for a drained and more efficient boiler:

1. Make necessary preparations

To drain your boiler safely, you will first need to unplug it from the mains and wait for the water inside the boiler to cool down. This is to make sure that there is no risk of scalding when water is being drained out. We recommend waiting at least 3 hours following the boiler being unplugged. You will also need to turn off the water intake valve – this will make sure no water enters the unit while you’re emptying it.

2. Find and prepare the drainage valve

Once your boiler is prepared and the water has cooled, you will need to find the drainage valve which is where you will let the water out. Usually, the drainage valve will be on the radiator that is positioned lowest in your home. The valve will likely be in the bottom corner of the radiator. Once you have located the valve, you will need to secure your hose onto it and ensure the other end of your hose is somewhere outside the home so that the water can be moved safely.

3. Open the valve and drain

Once your hose is tightly secured and in place, you can open the valve on the radiator and let the water drain out. You will need to leave the hose in place until there is no more water to drain. Once empty, you can close the valve and remove the hose.

4. Re-pressurise the boiler

The next step is to locate and open the braided filling loop which should be positioned underneath your boiler unit. The filling loop is a braided hose with fittings on each end; one connecting to the unit, the other connecting to the mains. To re-pressurise the boiler, all you will need to do is leave this open until the pressure dial reads 1. You can then put the filling loop back in place.

5. Make final checks

Finally, you can make any final checks around your boiler unit and radiators – if there are no leaks, you have successfully drained your Worcester Bosch Combi Boiler!