Overflow Pipe Dripping Outside a Bexley House: Causes

A small pipe dripping or running down the outside wall of your Bexley house is an overflow, and it is telling you a valve inside is not shutting off. If the pipe comes out near the eaves or roof line, it is usually the cold water tank or the small heating header tank in the loft. If it comes out lower down by the bathroom, it is the toilet cistern. In nearly every case the fix is a new float valve or washer, and you can stop the water in the meantime with the small isolation valve on the feed to that tank or cistern.

Why overflows run

Every cistern and open tank in a house has a float valve: a valve on the water inlet with a float that rises as the tank fills and shuts the water off at the right level. The overflow pipe is the safety net. If the valve does not close fully, the water level creeps up and spills out through the overflow, instead of over the top of the tank and through your ceiling.

So the overflow is doing its job. It is the valve that has failed.

Bexley’s water is hard: about 284 mg/l in Thames Water’s Bexley zone, which covers Old Bexley and North Cray, and about 359 mg/l, very hard, in the Bexleyheath zone next door. Scale on the valve seat and a hardened washer are the usual reasons a float valve stops sealing. A float that has filled with water or an arm that is bent are the other common faults.

Which overflow is it?

Go outside and look at where the dripping pipe comes out of the wall. Then go inside and find what is directly behind it.

High up, near the roof or eaves

• Cold water storage tank: a large plastic or older galvanised tank in the loft that feeds the cold taps upstairs and the hot water cylinder. It has a float valve on the mains inlet.
• Feed and expansion tank: a much smaller tank, also in the loft, that tops up an older open-vented heating system. If its overflow runs, the heating system may be pushing water back up, or the small float valve has failed.

Lower down, by the bathroom or toilet

• Toilet cistern: older toilets have an overflow pipe straight out through the wall behind the cistern. Most modern ones overflow inside, into the pan.

If you are still not sure, turn off the isolation valve on the toilet feed. If the outside drip stops within a minute or two, it was the toilet.

What to do, step by step

1. Identify which tank or cistern is overflowing, using the pipe’s position.
2. For a toilet, lift the cistern lid and check whether the water is above the overflow level.
3. For a loft tank, go up with a torch, keep to the joists and look in the tank.
4. Lift the float gently. If the water stops, the valve works but the float is set too high, or is heavy with water.
5. If the water keeps coming even with the float lifted, the valve washer or seat is worn or scaled.
6. Turn off the small isolation valve on the pipe feeding that tank or cistern.
7. If there is no isolation valve, or it will not turn, turn off the main stopcock.
8. Book a repair. A float valve or washer replacement is a short job.

Why not just leave it?

• It wastes water. On a meter, a constant overflow is paid for by the litre, every hour of every day.
• It can freeze. In winter, a dripping overflow can freeze at the end and block. The tank then fills to the brim, and if the valve keeps leaking, water comes over the top and through the ceiling. Joydens Wood, on the hill, and the cold lofts of Bexley’s bungalows are where we see this most.
• It stains and damps the wall. Water running down brickwork for months soaks into it, marks render and can feed damp inside.
• It can mean a heating problem. If the small heating header tank overflows, it may be a failed valve, but it can also be a sign that water is getting into the heating system from the hot water cylinder through a failed coil. That is worth a proper look.

Bexley houses and their tanks

• Old Bexley village houses: older tanks, sometimes still galvanised steel, and float valves that may be decades old.
• 1930s semis at Coldblow and towards Bexleyheath: a cold tank and a small heating tank side by side in the loft, overflows out at the eaves.
• Joydens Wood bungalows and post-war houses: tanks in a cold roof space, and a long climb for the water main up the hill.

If your house has a combi boiler and a mains-fed system, there may be no loft tanks at all, in which case an outside overflow is almost always the toilet.

Can I fix it myself?

Toilet fill valves are often simple to clean or replace if you are handy. Loft tank float valves are similar, but working in a loft is awkward and a dropped spanner in a tank is common. If you are not comfortable, call us. If the feed has no isolation valve, we will fit one at the same time so this is easier next time.

Running toilets have the same scale problem. Our guide to why a toilet keeps running in Sidcup goes through the toilet side in more detail.

When to call

Call us if the overflow is running fast, water is coming through a ceiling, you cannot find or turn an isolation valve, or the heating tank overflows. We handle overflowing toilets and tanks in Bexley and dripping taps in Bexley. More on the area is on our Bexley area page.

Need a plumber now?

Call 07868 281022 and tell us your postcode, where the overflow pipe comes out, and whether you have managed to turn the water off. We agree the price with you before any work starts.