No Hot Water Repair (Combi Boilers)

Checks you can safely do before calling

A combi only makes hot water while a tap is running, so a few outside causes stop it completely. Work through these first. Every one is done from outside the boiler; the casing stays shut.

• Is it every hot tap or just one? One tap or shower with no hot water points to that tap or mixer valve, not the boiler.
• Read the display. A fault code or a flashing light tells an engineer a lot; note it down before resetting.
• Check the pressure gauge. A cold combi normally sits between 1 and 1.5 bar. If it falls well below 1 bar, many models refuse to fire and show a low-pressure fault.
• After a hard frost, follow the white plastic pipe from the boiler to the outside drain. Ice inside it blocks the condensate and locks the boiler out; a kettle of warm (never boiling) water along the pipe usually thaws it.
• Reset once, using the reset button. If the fault returns, stop resetting and call.

Smell gas while you are checking? Stop, get windows open, shut the meter valve if it is safe to reach, avoid switches, get everyone out, then ring 0800 111 999 before anyone else.

Worcester combi with no hot water: what to look at

On many Worcester Greenstar combis the ECO button controls preheat. With ECO lit, the boiler does not keep water warm in readiness, so hot water takes longer to come through. Nothing is broken; the boiler is simply heating from cold. The temperature knob or setting may also have been turned down; check it before booking anything.

Warm radiators with cold taps points first at the diverter valve. It switches the boiler’s heat between the radiators and the plate heat exchanger, and when its motor or cartridge sticks in the heating position you get warm radiators and cold taps. Hot water that only arrives when the heating is also on points the same way. Our guide to no hot water from a Worcester boiler goes through the Worcester symptoms one by one, and the Worcester fault codes list covers what the display is telling you.

Why a combi boiler stops heating water

If the boiler does not fire at all when you open a hot tap, the flow sensor is often the cause. It detects water moving through the boiler, and if debris jams its small turbine or the sensor fails, the boiler never knows a tap is open. Some combis also need a minimum flow before they fire, so a tap barely cracked open may not start them.

If the water comes through lukewarm, or swings between hot and cold, the plate heat exchanger is the likely cause. London’s hard water leaves scale in its narrow channels, which cuts the heat transfer. Our page on lukewarm hot water from a combi covers that symptom on its own, and heating on but no hot water covers the diverter side.

The engineer does not guess between these. With a tap running they check whether the flow sensor registers, whether the diverter moves, and what temperatures go in and out of the heat exchanger. Gas work is carried out by Gas Safe registered engineers.

What combi hot water repairs usually cost

The £60 call-out covers getting an engineer to you at any hour, and the repair price is agreed with you on site before any work starts. See what an emergency plumber charges for how that works.

As a guide to the London market, a replacement diverter valve or actuator, a flow sensor, or a new plate heat exchanger each typically costs somewhere in the low-to-mid hundreds of pounds fitted, depending on the make and how easy the part is to reach. Clearing a frozen condensate pipe or rebalancing pressure is at the cheaper end. If your boiler is old and several parts are failing, the engineer will tell you plainly whether a repair is worth it.