Emergency repairs
Overflowing Water Tanks
An overflow pipe dripping outside, or water pooling in the loft, usually means a storage or feed tank is overfilling. Because these tanks sit at the top of the house, a failure can bring water through the ceilings below, so a quick repair matters.
What to do while you wait
When a tank is overflowing, stopping the water going into it is the priority, but your safety in the loft comes first:
- If you can reach the tank safely, close the isolating valve or gate valve on the pipe feeding it to stop more water coming in.
- If you cannot reach or isolate it, close the main stopcock to cut the supply to the whole property.
- Do not go up if the loft is unlit, poorly boarded or feels unsafe. Water, electrics and an awkward space make a dangerous mix.
- If water is reaching ceilings, light fittings or electrics, keep clear and switch off at the consumer unit when it is safe to do so.
- Catch the drips below with buckets and towels, and move anything that can be damaged out of the way until help arrives.
Our guide to turning off your water supply shows where the stopcock usually sits and how to use it.
What do these tanks do, and why do they overflow?
Many UK homes, especially those with a traditional hot water cylinder, have one or more water tanks in the loft. A cold water storage tank holds the water that feeds the bathroom cold taps, the toilet and the hot water cylinder, while a smaller feed and expansion tank tops up a vented heating system. Each one fills through a float valve, often called a ball valve, which is meant to shut the incoming water off once the level is right.
An overflow starts when that valve stops closing as it should. The washer inside it wears, the pivot sticks, or the float fills with water and sinks, so the valve never seats. Water keeps flowing in, the level climbs past the normal mark, and the excess runs out through the overflow pipe, the one you may notice dripping or running on an outside wall. That overflow is a deliberate safety outlet, sending surplus water outside instead of into the house, so a running overflow is a clear signal that the valve has failed and needs attention.
The reason to act quickly is where the tank sits. Perched above the living space, a tank that overflows faster than its pipe can carry away, or whose overflow has blocked, can spill into the loft and soak down through ceilings, insulation and light fittings. Catching the fault while the overflow is still coping is far less trouble than dealing with a collapsed ceiling afterwards.
Warning signs
Signs a tank is overflowing
A dripping overflow pipe
Water running or dripping from a pipe on an outside wall, often up near the eaves, is the classic sign of a tank filling past its proper level.
Running water in the loft
Water trickling or a valve hissing away in the loft when no taps are in use is a tell-tale sign of a valve that will not shut off.
Ceiling stains or damp
A spreading stain, bulging plaster or damp on an upstairs ceiling can mean a tank has already overflowed into the loft and needs urgent help.
The repair
How do we put it right?
With the inflow stopped, repairing an overflowing tank is usually a straightforward part of our emergency plumbing work. We isolate the tank, repair or replace the failed float valve, and check that it shuts off cleanly at the correct level.
- Isolate the tank and inspect the float or ball valve
- Renew the washer, or fit a new valve and float where needed
- Check the water level, the tank lid and the overflow pipe
- Refill and confirm the valve shuts off cleanly before we leave
Related problems worth checking
A tank fault seldom sits on its own. If you have spotted other symptoms, these pages may help:
- Burst pipe repairs, if a pipe to or from the tank has split
- Water pressure problems, if a gravity-fed supply has turned weak or erratic
- Stopcock repairs, if the stopcock has seized and you could not isolate the supply
Frequently asked questions
Overflowing tanks, answered
Why is water dripping from an overflow pipe outside my house?
A dripping or running overflow pipe outside usually means a tank inside is overfilling, most often the cold water storage tank in the loft or a smaller feed tank. The overflow is a safety outlet that carries excess water outside instead of letting it spill into the property. It is doing its job, but it also tells you a float or ball valve has failed to shut off the incoming water and needs repair.
Is an overflowing loft tank an emergency?
It should be treated as urgent. While the overflow pipe is working, excess water goes outside, but if the overflow cannot cope or becomes blocked, the tank can spill into the loft and bring water through the ceiling below. Because the tank sits at the top of the house, a failure there can cause widespread damage, so it is best to isolate the supply to the tank and arrange a repair quickly.
How do I stop a tank overflowing while I wait?
If you can safely reach the tank, there is often an isolating valve or gate valve on the pipe feeding it that you can close to stop more water entering. If not, turning off the main stopcock will stop the supply to the whole property. Do not go into a loft if it is unsafe, poorly boarded or unlit. Once the inflow is stopped, contact us for help so the faulty valve can be repaired or replaced.
What causes a water tank to overflow?
The usual cause is a worn or stuck float valve, also called a ball valve, which is meant to shut off the water when the tank is full. Over time the washer wears, the arm sticks, or the float fills with water and sinks, so the valve never closes and the tank keeps filling until it overflows. We repair or replace the valve and check the tank, its lid and the overflow so it works safely again.
Tank overflowing or overflow pipe dripping?
Email our team for immediate help and safety guidance, or request a call back and we’ll arrange for the faulty valve to be repaired.