Hot Water Problems: No Heat, Not Enough, Or Something Smells Off

Usually a harmless reaction between the magnesium anode in your cylinder and sulphate bacteria in the water, more noticeable after the cylinder’s sat unused. Running the hot tap for a few minutes often clears it; if it persists, worth having the anode checked.

Not usually dangerous for washing, but it’s a sign of sediment or corrosion inside the cylinder that’s worth investigating, especially if it doesn’t clear after running the tap for a minute or two.

This often points to a failing diverter valve not holding position properly, or in some cases a flow sensor issue causing the boiler to briefly lose its reading on how much water is passing through.

Yes — a combi heats water on demand at a fixed maximum rate, so running two hot outlets at once splits that capacity between them, meaning both run noticeably cooler than either would alone.

Normal to some extent on long pipe runs, since the water sitting in the pipe has to be pushed through and cooled water cleared first. If it’s got noticeably worse recently, that’s more likely a pressure or flow issue worth checking.

It should be set to 60°C for both comfort and legionella safety. If you’re not sure what it’s currently set to, this is worth checking at your next service rather than guessing.

Yes — North London’s hard water accelerates limescale build-up inside heat exchangers and cylinder coils, one of the more common causes of gradually weakening hot water performance over several years.

On a cylinder system, this points to the cylinder not having fully reheated between uses, often because the reheat schedule or immersion backup isn’t keeping pace with household demand.

Possibly — if you’re consistently running out of hot water during busy periods like mornings, an undersized cylinder for the household’s current size is a common and fixable cause worth discussing with an engineer.

In a hard water area like North London, a softener can meaningfully slow limescale build-up inside heat exchangers, cylinder coils and immersion elements, which may extend their working life. It’s a genuine investment rather than a quick fix, and won’t reverse existing scale — more relevant for protecting a newer system than solving an existing fault.

Showers generally use less hot water per use than a bath, so switching can ease demand on a system struggling to keep up, particularly a smaller combi or undersized cylinder. It won’t fix an underlying fault, but for a system that’s simply borderline for the household’s needs, it can meaningfully reduce how often you notice its limits.