Baxi Boiler No Hot Water: Causes and What to Check

Is it a Baxi combi or does it feed a cylinder?

Baxi make combis, system boilers and regular boilers, and the current 200, 400, 600 and 800 ranges, along with older names such as the Duo-tec and Platinum, cover all three. The words combi, system or heat only on the front panel or data badge tell you which one is on your wall.

If you have a hot water cylinder in an airing cupboard, you are not on a combi. That changes where the fault is likely to be. On a combi, the hot water is made inside the boiler, so no hot water is a boiler repair. On a system or regular boiler, the boiler only heats the cylinder when asked, and the fault is very often in the controls or valves outside it.

E119 and other codes: what the display is telling you

Baxi displays show a code starting with E when the boiler has stopped itself. Note the full code before touching anything. It is what an engineer needs first, and a reset wipes it.

E119 is the one most people see alongside no hot water, and it usually means the water pressure in the heating system has dropped too low for the boiler to run safely. Check the pressure gauge. If it reads well under 1 bar with the boiler cold, top it up through the filling loop as your manual describes, then reset. If it drops again within days, there is a leak or a failing expansion vessel on the heating side, and topping up repeatedly only hides it. If the pressure is too high instead, our guide to boiler pressure too high explains why.

E133 means the boiler tried to light and could not, often because the gas supply is off, a prepayment meter has run out, or the condensate pipe has frozen. Our page on the Baxi E133 fault code goes through the full list of causes. Reset once or twice at most. A code that keeps coming back is the boiler protecting itself.

If the name on the front says Potterton rather than Baxi, the same codes usually apply, because both brands come from the same maker, and our guide to Potterton boiler no hot water covers those models, including the older heat only boilers that feed a cylinder.

Checks to make before booking anyone

These cost nothing and clear a fair share of Baxi no hot water calls.

If only some taps have lost their hot water, the boiler is probably fine, and our guide to no hot water upstairs or at one tap is the better place to start.

• Pressure: around 1 to 1.5 bar cold is typical for a sealed system. Low pressure stops many Baxi boilers firing at all.
• Gas: light a hob, if you have one, to prove the supply.
• Hot water setting: check the hot water temperature control on the boiler has not been turned down to minimum or switched off.
• Programmer: on a system or regular boiler, make sure the hot water channel is on. A power cut can reset it.
• Condensate: in freezing weather, check the plastic condensate pipe outside. Thaw it with warm, not boiling, water.
• More than one tap: hot at one outlet but not another is a tap or valve problem, not the boiler.

Baxi combi: heating works but no hot water

With no code on the display and hot radiators, a Baxi combi has almost always failed in one of three places. The diverter valve is the part that swings the boiler's output from the radiators to the hot water when you open a tap. Stuck on heating, you get hot radiators and cold taps. Stuck partly across, you get radiators warming in summer and hot water that never gets properly hot. Our guide to diverter valve replacement cost explains what that repair involves.

The flow sensor tells the boiler a tap is open. When it fails, the boiler stays silent as you run the hot tap, yet fires normally for the heating. Debris in the small filter on the cold inlet can have the same effect by cutting the flow below what the sensor needs to see.

The plate heat exchanger is where the heat passes into the tap water, and in London it scales up steadily. Water that starts warm and fades, or a boiler that lights and cuts out while the tap runs, points here. The same three parts fail on most combis, and our guide to no hot water from a combi boiler covers them in more depth.

Hot water goes hot, then cold, on a Baxi combi

Water that runs hot for a short while and then turns cold, or swings between hot and cold, is a common complaint. Before anything else, open the tap further. A trickle can fall below the flow the boiler needs to keep firing, especially on a mixer tap set halfway. If a proper flow still cycles hot and cold, the usual causes are scale in the plate heat exchanger or a flow sensor that is dropping in and out, and both need an engineer to confirm with temperature readings rather than a guess.

No hot water from a Baxi system or regular boiler

With a cylinder, the Baxi may be working perfectly and never being told to heat the water. The call goes from the programmer to the cylinder thermostat, then to a motorised valve that opens the route to the cylinder coil and signals the boiler to fire. If any link fails, you get heating and no hot water.

The motorised valve is the most common failure, its motor or switch wearing out with age. A cylinder thermostat can fail or be knocked down. If the cylinder has an immersion heater, switching it on is a useful test: if it gives you hot water, the cylinder is fine and the fault is on the boiler side. Our guide to no hot water but the heating works goes through these checks on an unvented or tank fed cylinder.

What an engineer checks, and repair or replace

We start with the code history and pressure, then prove each part of the hot water circuit in order: on a combi, the flow sensor, the diverter valve and the temperatures across the plate heat exchanger; on a system boiler, the call for heat, the motorised valve and the cylinder thermostat. Parts are only changed once they are proved faulty.

Most Baxi hot water faults are ordinary repairs. Replacement becomes the sensible recommendation when the boiler is old, parts are scarce, or the same failure keeps returning because scale or sludge has not been dealt with. A boiler diagnosis visit gives you that answer with evidence behind it.

Removing the case of a gas boiler is gas work and must be done by a Gas Safe registered engineer, and that includes the diverter valve, the flow sensor and the plate heat exchanger. If you smell gas, turn it off at the meter, open windows and call the gas emergency line on 0800 111 999.

When to call us

Call us on 020 4652 5111 or send an enquiry if an E code returns after a reset, if the pressure keeps falling after you top it up, if the boiler or the pipes under it are dripping, or if the taps still run cold after the checks above. The model name and any code on the display help us bring the right parts. We have 20 engineers across London, and our rate is on the pricing page, agreed before anyone attends.