No hot water but the heating works? Common causes

Updated 6 November 2026

If the radiators get hot but the taps run cold, the boiler itself is usually fine: it's lighting and burning gas. The fault is in the part that sends heat to your hot water instead of the radiators.

First, which boiler do you have?

• Combi boiler: no hot water tank. Hot water is heated on demand when you turn on a tap. Most Newcastle flats and terraces have one.
• System or regular boiler: there's a hot water cylinder in an airing cupboard, with a programmer that has separate heating and hot water settings.

Checks you can do safely

1. Check the hot water setting. On a system boiler, make sure the programmer has hot water switched on, not just heating. After a power cut the clock may have reset.
2. Check the boiler pressure. Most combis want 1 to 1.5 bar on the gauge when cold. Low pressure can stop hot water first. See why a boiler loses pressure.
3. Try a different tap. If one tap is cold and the rest are hot, it's the tap or a mixer valve, not the boiler.
4. Turn the hot water temperature up on the boiler itself. Someone may have knocked the dial.
5. Look for a fault code on the display and note it down. Our fault code guide explains the common ones.

The usual faults

• Diverter valve (combi). This valve switches the boiler's heat between radiators and taps. When it sticks, you get heating but no hot water. It's one of the most common combi repairs.
• Plate heat exchanger (combi). It heats your tap water. In hard-water areas it scales up, but Newcastle's water is soft, so this is less common here than in the south.
• Motorised valve or cylinder thermostat (system boiler). These control water flowing to the cylinder and wear out over time.
• Flow sensor (combi). It tells the boiler a tap is open. If it fails, the boiler never fires for hot water.

What it costs

Most of these repairs cost £150 to £450 including parts, depending on the boiler and the part. A Gas Safe engineer will diagnose it on the first visit and tell you the price before fitting anything. Don't open the boiler casing yourself: only a Gas Safe registered engineer can work on the gas side of a boiler.

Need it sorted? Boiler repair in Newcastle typically costs £150 to £450. A local engineer will give you a price before starting.