Same-Day Boiler Repair in Sutton

The Brief

A homeowner in Sutton woke up on a cold January morning to find there was no hot water at the taps. The central heating itself was running fine and the radiators were warming up as normal, but the shower and the kitchen tap were cold. They logged a call with us before 9am.

Heat working but no hot water is a classic Vaillant combi symptom and almost always points at the diverter valve. The valve is the part that switches flow between heating the radiators and heating water for the taps, and when it sticks shut on the hot-water side you get exactly this picture.

What We Did

The visit ran in this order:

• Visual and diagnostic checks: ran the boiler through a heating call and a hot-water call, watched the fault behaviour, and pulled live readings off the control board to confirm what the unit was reporting.
• Isolated and pressure-tested: dropped pressure off the system safely, isolated the gas and water, and pressure-tested around the valve assembly to rule out a leak or a blockage further down the line.
• Identified the diverter valve fault: confirmed the diverter cartridge was sticking and not switching across to hot-water demand, exactly as the symptoms suggested.
• Sourced the matching part: rang our local Vaillant supplier in south London and collected the correct cartridge for that model the same morning.
• Fit the replacement: stripped down the diverter housing, fitted the new cartridge with fresh seals, and rebuilt the assembly to manufacturer spec.
• Re-pressurised the system: brought system pressure back up to the correct cold-fill range and bled out any trapped air at the radiators and the boiler itself.
• Full safety re-check: ran a gas tightness test, checked flue gas readings, and went through the standard Gas Safe sign-off on the rebuilt unit.
• Long flush cycle: left the system running through a long hot-water cycle to confirm the new diverter was switching cleanly under load and that hot water was holding steady at the taps.

The Result

Hot water was back at the taps the same afternoon. No follow-up calls, no return visits, no surprise add-ons on the invoice. The customer paid the standard in-warranty repair rate for a same-day part fit, well inside our usual £100 to £500 plus VAT band for boiler repairs.

Worth noting: a sticking diverter valve on a Vaillant combi is common enough that we now carry similar cartridges and seal kits in the van as standard. Next time we get a call like this on a Vaillant in Sutton, Wimbledon or anywhere else on the patch, the part is more often than not already on board, which keeps repair times down to a single visit.

Time on site: 2 hours from arrival to a fully tested, signed-off boiler.

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