No Hot Water? Step-by-Step Guide to Finding and Fixing the Problem

Start Here — Quick Checks Before Anything Else

Before calling a plumber, work through these checks in order. Most no-hot-water situations have a straightforward cause that you can identify in five minutes.

Check 1: Is the boiler on?

Check the boiler display. Is it showing a fault code, a flashing light, or is it completely blank? If the display is blank, check the boiler is plugged in and the fuse in the spur switch has not blown.

Check 2: Is the pressure too low?

Look at the pressure gauge on the boiler. If it reads below 1 bar, the boiler has likely locked out due to low pressure. See our guide on how to repressurise your boiler — this often restores both heating and hot water immediately.

Check 3: Is the pilot light out? (older boilers)

On older non-condensing boilers, a blown pilot light will stop both heating and hot water. Follow the manufacturer's instructions to relight it — usually a button on the boiler body. If it will not stay lit, call a Gas Safe engineer.

Check 4: Check the thermostat settings

Confirm your programmer or smart thermostat is set correctly for hot water. It is surprisingly common for a schedule to have been accidentally changed — particularly after a power cut resets some older programmers.

Check 5: Is it affecting heating too?

This distinction matters for diagnosis (see below).

No Hot Water BUT Heating Is Working Fine

If your radiators are warming up normally but you have no hot water from taps or showers, the problem is most likely in the hot water circuit specifically — not the boiler overall. Likely causes:

Faulty Diverter Valve (Combi Boilers)

Combi boilers use a diverter valve to switch flow between the heating circuit and the hot water circuit. If this valve sticks or fails, the boiler may heat the radiators but fail to deliver hot water to the taps. You may also notice the hot water runs briefly then goes cold. This is a relatively common fault requiring a Gas Safe engineer to replace the valve.

Hot Water Cylinder Not Heating (System Boilers)

If you have a system boiler with a hot water cylinder, check the cylinder thermostat and the immersion heater. The motorised valve that directs hot water to the cylinder may have failed. Check the cylinder is warm to the touch — if it is stone cold despite the heating working, the motorised valve or the cylinder stat is likely at fault.

Scale Build-Up in the Heat Exchanger

In hard water areas like Peterborough, limescale builds up inside the boiler heat exchanger over time. This restricts hot water flow particularly at the hot water taps (you may notice hot water at low flow but cold at high flow). A power flush or descaling treatment can address this.

No Hot Water AND No Heating

If both heating and hot water have stopped working, the issue is most likely with the boiler itself. Check the boiler display for a fault code and consult the manufacturer's troubleshooting guide — many fault codes point to specific components. Common causes include:

• Low system pressure (top up using the filling loop)
• Frozen condensate pipe (in very cold weather — the white plastic pipe exiting the boiler outside may have frozen)
• Ignition failure (the boiler is trying to fire but cannot ignite the gas)
• Fan or pump failure
• Gas supply interrupted (check if other gas appliances are working)

Frozen Condensate Pipe — A Winter-Specific Problem

Modern condensing boilers produce acidic condensate water which drains away through a plastic pipe. In very cold weather — which does happen in Peterborough winters — this pipe can freeze, causing the boiler to lock out. You will usually see a fault code and the pipe will visibly frost over.

To thaw it yourself: pour warm (not boiling) water along the length of the pipe outdoors. Once cleared, reset the boiler. Consider insulating the pipe to prevent a repeat.

When to Call an Emergency Plumber in Peterborough

Call a professional immediately if:

• You can smell gas near the boiler — evacuate and call the National Gas Emergency line on 0800 111 999 before calling a plumber.
• The boiler is making unusual banging, popping, or hissing noises.
• There is any sign of water around or inside the boiler casing.
• You have tried repressurising and resetting and the boiler still will not fire.
• You have no hot water or heating with young children, elderly occupants, or medical conditions in the property.
• You are a landlord — loss of hot water and heating is a legally urgent repair under the Landlord and Tenant Act 1985.

Emergency Plumbing in Peterborough

Our qualified Gas Safe engineers are available for same-day call-outs across all Peterborough postcodes (PE1–PE7) and surrounding areas including Werrington, Bretton, Orton, Hampton, Yaxley, Whittlesey, Stamford, and Market Deeping. We carry replacement diverter valves, thermostats, and motorised valves on every van — most no-hot-water faults are resolved in a single visit.