Vokera Boiler No Hot Water: Causes and What to Check

Heating works, hot water does not: why that matters

Turn the heating on and feel a radiator. It is the single most useful thing you can do before calling anyone, because it splits the fault in two.

Hot radiators prove the gas supply, the burner, the fan, the ignition and the pump are all working. What is left is the small group of parts that only come into play when you open a hot tap. Cold radiators as well as cold taps mean the boiler is not running at all, and the display, the pressure gauge and the gas supply are where to look.

Read the display and the gauge

Vokera models such as the Unica, Vision, Compact, Easi-Heat Plus, Linea and Mynute show faults in different ways depending on age. Newer ones show a code on the display, older ones use flashing lights. Either way, note exactly what you see before resetting, and look the code up in the manual for your model, because codes are not the same across every Vokera range.

Then check the pressure gauge with the boiler cold. Around 1 to 1.5 bar is normal for most sealed systems. Well below 1 bar and most Vokera boilers will refuse to run. Top up through the filling loop as the manual describes and reset once. If the pressure keeps falling, water is leaking from the heating circuit somewhere, or the expansion vessel has lost its charge, and that needs finding. Pressure that climbs too high when the boiler heats up is a different problem, covered in our guide to boiler pressure too high.

Things to check yourself

These are safe to do and clear a fair number of calls.

• Open the hot tap fully. A combi needs a minimum flow to fire, and a mixer half open or a scaled aerator can fall short of it.
• Try more than one tap. If only one outlet runs cold, the boiler is fine and the fault is at that tap or shower.
• Check the hot water temperature control on the boiler has not been turned to minimum or off.
• Light a hob, if you have gas cooking, to prove the gas supply.
• In a freeze, check the white plastic condensate pipe outside. A frozen one stops the boiler, and warm, not boiling, water thaws it.

The hot water flow switch

Vokera combis rely on a flow switch to tell them you have opened a hot tap. Water moving through it lifts a small paddle or magnet, which triggers a switch, and the boiler then swings the diverter to hot water and fires. If the paddle sticks or the switch fails, the boiler simply never sees the demand. You run the tap, nothing happens, yet the heating fires normally. That pattern points here more than anywhere else.

Sometimes the switch is fine and the flow is not. Scale, debris or a blocked inlet filter cut the flow below what the switch needs to see. This is common in London, where hard water leaves scale in every small passage. It is why the engineer checks the flow through the boiler before condemning the switch.

The diverter valve

The diverter valve directs the boiler output either to the radiators or to the plate heat exchanger that heats your tap water. On Vokera boilers it is part of the hydraulic assembly at the bottom of the case, driven by a small motor or actuator. When it sticks on heating, you get hot radiators and cold taps. When it sticks partly across, radiators warm up whenever you run a hot tap, even in summer, and the hot water is only ever lukewarm.

Sometimes only the actuator has failed, sometimes the valve itself, and the repair differs, so it is worth having it diagnosed rather than parts swapped in turn. Our guide to diverter valve replacement cost explains what the job involves.

A scaled plate heat exchanger

The plate heat exchanger is a stack of thin plates where the heat from the boiler passes into the water going to your taps. Scale builds up between the plates and slows that transfer. The symptoms creep in over months: water that is hot at first and then fades, a boiler that fires and cuts out while the tap runs, or water that only gets properly hot at a trickle.

The same symptoms can come from a flow switch dropping in and out, so the engineer measures the temperatures across the plate before deciding. A badly scaled plate is usually replaced, not flushed, on an older boiler. Our guide to no hot water from a combi boiler goes through how the three faults above are told apart.

Repair or replace a Vokera?

A flow switch, diverter valve or plate heat exchanger is a standard repair on most Vokera combis, and parts for current models are easy to find. The question gets harder on an older boiler that has already had several repairs, where parts are becoming scarce, or where scale or sludge has damaged more than one part. In those cases we give you the diagnosis and the choice, and a boiler diagnosis visit is the way to get it with evidence rather than a guess.

Taking the case off a gas boiler to reach the flow switch, diverter or plate heat exchanger is gas work and must be done by a Gas Safe registered engineer. 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 the taps still run cold after the checks above, if the pressure keeps dropping, if a fault code comes back after a reset, or if you can see water under the boiler. Give us the model name from the front of the boiler and any code or light pattern. We have 20 engineers across London, and our rate is on the pricing page, agreed before anyone attends.