How to Drain a Central Heating Boiler

A central heating boiler may need to be drained for repair or cleaning purposes. Old boilers accumulate sludge, which decreases their efficiency as a heating system and requires. In addition, you might also want to replace broken valves and seals to stop your boiler from leaking. In both these cases it is essential to first drain the boiler from water. The steps below will guide you through draining an open vented system and a combination boiling system.

Tools and Materials Required

•    A spanner to pry open valves
•    A 20 inch or 50 cm piece of wood
•    A rubber hose
•    A box of matches and
•    A cleaning rag

Step 1 – Take Appropriate Precautions

Before starting work of any kind, turn all thermostats to zero and power off the boiling system. This can be done either by removing the plug, if it is an electric powered system or by shutting off the gas inlet, if it is a gas powered system.  This is done to ensure that you don’t electrocute or burn yourself. Always keep a cleaning rag in hand to wipe the valves before opening them. This will ensure that your spanner can get a strong hold on the otherwise greasy valves. With these precautions in mind, get ready to use some elbow grease.

Step 2 – Getting Your Open Vented Boiler Ready for Drainage

If you have an open vented system, you will need to block the inlet valve to stop the water from filling up the boiler. This can be done by using the piece of wood to raise the ball valve up to a position where it blocks the inlet and hence stops the flow of water. The position of the drain tap depends on your boilers design but is generally found on the lower side. Slide a hose on this outlet. If it does not fit properly, use a lighted match to heat and make flexible the diameter of the hose to ensure a proper fit. Guide the drainpipe outside to a drain and ensure that the water properly enters a drainage system and doesn’t flood an area. If you don’t have an open vented system, read step 3.

Step 3 – Getting Your Combination Boiler Ready for Drainage

Combination boilers have an inlet valve that can be easily closed off by a spanner to cut off water supply. These boilers also have a drain tap and can be prepped for drainage much in the same way as an open vented system was in the previous step.  After you have done this, its time start draining.

Step 4 – Draining the Boiler

Open the manual control or locksheild valve to start draining. The water will run out of the drain tap and into the drain. While the water drains, locate the radiator that is furthest and highest from the boiler and open the bleed valves. Only loosen them a little to check if water flows out of them; fully open them if it doesn’t. Do this with every radiator in the house starting from to one farthest and ending with the nearest to the boiler. Bleed valves allow air to enter the water piping which pushes the water out the drain outlet. You are good to clean or repair the boiler once water stops flowing out of the drainpipe.