Water where it should not be? Shut it off, then let us take it from there

Before anything else, find the stopcock and turn it clockwise until it stops. In most London homes it is under the kitchen sink; in flats it may be in a hallway cupboard, a utility cupboard on the landing or a boxed-in riser. If water is near electrics, switch the affected circuit off at the consumer unit, or the whole board if you are not sure which. Open the cold taps to drain the pipework down. Put something under the drip. Move what can be moved.

If the stopcock will not turn, do not fight it with a wrench. Look for an external stop valve under a small cover in the pavement or front garden, or ask the building manager for the riser valve. If the water is from the heating system rather than the mains (the boiler pressure gauge dropping is the tell), turn the boiler off so it stops trying to run with no water.

Then send the details: what is leaking, where, whether it has stopped with the stopcock, and whether it is affecting a neighbour. That is what decides what goes on the van.

Emergency cover runs outside normal hours for the failures that genuinely cannot wait until morning. When you make contact you get a straight answer about how soon someone can be with you and what the out-of-hours price is, before you commit. What you will not get is a promise of a time that cannot be kept; a realistic window that is honoured is worth more at eleven at night than an optimistic one that is not.

Not everything that feels urgent needs an out-of-hours visit, and you are told when it does not. A dripping tap, a slow drain or a radiator that is cold can wait until the morning at the daytime price, and if the stopcock has stopped the leak, so can many leaks. Water through a ceiling, sewage backing up, no water at all or a leak that cannot be isolated are the ones worth a night call.

Burst pipes in London are usually one of three things: a frozen and split pipe in an unheated loft or outside wall, a compression joint that has worked loose over years of expansion and contraction, or a plastic push-fit that was never fully inserted and finally let go. The emergency repair isolates the section, cuts out the damage and remakes it in copper or a properly inserted push-fit, then pressure tests it before the water goes back on.

Where the leak is hidden, under a floor or behind a tiled wall, the emergency visit isolates it and gets the rest of the property working again. Finding it without wrecking the room is a leak detection job for the daytime, with the right equipment.

Seized stopcocks are an emergency in themselves. If yours will not turn, having it replaced with a lever valve during a planned visit is one of the cheapest bits of insurance a property can have.

No heating in January with young children or an elderly relative in the house is an emergency. So is a boiler leaking water onto the floor, a cylinder that has split, or a boiler making a noise that sounds wrong. The engineer who attends is the same one who does boiler repairs, so the visit is diagnosis and repair where the part is carried, or a safe isolation and a quoted return where it is not. Heating that has failed because of a system fault, such as a pump, a zone valve or an airlock, is often fixed on the spot.

A smell of gas is not a plumbing emergency; it is a gas emergency. Turn the gas off at the meter, open windows, do not switch anything electrical on or off, and call the National Gas Emergency number, 0800 111 999. The repair follows once the supply is safe.

Sometimes the right answer at midnight is to make it safe and finish it in daylight. A cracked cistern is isolated and the flat gets its water back; the replacement cistern comes the next day. A leaking cylinder is drained and bypassed so the cold water works; the new cylinder is quoted properly. A split pipe in an awkward place gets a temporary repair clamp and a permanent joint when the wall can be opened. You are told which it is, what the permanent fix is and what it costs, before you agree to anything.

Emergency work is priced before it starts, like everything else. Out-of-hours visits carry a higher call-out price than daytime ones, and that price is stated when you get in touch, so the decision to have someone out at night is yours with the number in front of you. The price covers attending and the first hour of work; if the repair needs more time or parts, that is agreed before it continues. The invoice lists what was done and what was fitted, which is what a landlord, an agent or an insurer needs.

Because the answer on the phone is honest. Because the price is known before the van moves. Because the plumber who turns up also does heating, so a boiler leak and a burst pipe are one visit, not two firms. And because the temporary fix is explained as a temporary fix, with the permanent one quoted, rather than dressed up as the job being done.