We’ve all been there, you get home from work and your header tank is overflowing and water is cascading down the outside of your house. Don’t panic, there are lots of reasons and solutions to fix a problematic, overflowing header tank, so read our quick guide to diagnosing and fixing the problem sharpish. 

My header tank is overflowing – why? 

Your header tank is an essential part of your regular boiler heating system and is most likely in your loft, to make use of pressure and gravity to force the water through the system. It holds the cold-water supply to feed into your central heating system, houses the expansion from your hot water tank caused when your water heats up, and acts as a reserve supply if your mains supply ever fails, used for hot water supply only. 

It is connected to an overflow pipe, so if the water does overflow it drains outside your house rather than gushing back into the loft. So, if your header tank is overflowing and the overflow pipe is leaking water to the outside of your house – at least ‘Plan B’ is working, water is being safely diverted outside, and your loft won’t be flooded. 

My Header Tank Is Overflowing – Three Quick Fixes

  • Empty excess water. You can empty excess water out of the cold-water tank by running the hot taps for a while. Before long, you should see a reduction in the amount of water pouring from the overflow pipe, eventually dwindling to nothing. 
  • Drain the tank. This will require some skill, so if you’re unsure, call a plumber. First you need to cut off the supply by turning off the mains stopcock or rising main, then turn on the hot taps. When the taps stop running, your cold-water tank is empty. This is a great opportunity to clean out your tank and do some general tank maintenance if you need to. 
  • Reset the ballcock level. While your tank is empty, check the ballcock is at the right level. It should be about 1 inch below the overflow. You can carefully bend the ballcock arm to the right place. When you’re done you can refill the tank. 

What Can Go Wrong with Your Ballcock?

In most tanks, the water level is controlled and maintained by a float or ballcock valve which tells the system when the water is low or at the right level. 

The most common cause of an overflowing header tank is a fault with the float mechanism, which may not be rising to the correct level and therefore not stopping the supply of water to the tank. This causes it to overflow through the outlet pipe (causing that cascade of water!). So, what’s the problem? 

  • Your float has developed a hole. A hole in your ballcock float means it will fill with water before rising. It will sink or not provide enough pressure to close the valve, leaving your tank filling with water, way past the required level, thus activating the overflow.
  • Your washer has failed. If the rubber washer which seals off the valve has disintegrated or failed in any way, it will not create a watertight seal and the valve will not operate correctly. 
  • The brass nipple in the valve has excessive wear.  When sufficiently worn, the brass nipple will not create a seal, the valve will not operate properly, and your tank will continue to fill. 

Do I Need a Heating Engineer or Plumber? 

If you’ve tried the easy fixes above, and your header tank is still overflowing, it is time to send for the professionals. Here at Rowlen we have expert domestic plumbers and heating engineers who can identify the problem quickly and safely, carrying out effective repairs, which will save you time and money in the long run – give us a call today!