Radiators hot but taps running cold? It's one of the most common combi boiler faults, and it rarely means a new boiler. Simon walks through the six usual causes, from a stuck flow turbine to a scaled-up plate heat exchanger, plus the checks you can safely make yourself before calling anyone.

A wireless thermostat can look like it is working perfectly while the boiler never hears a thing. Here is how to tell a control fault from a boiler fault before you pay to replace the wrong one.

One fault code, at least seven possible causes: ignition electrodes, ignition lead, ignition module, PCB, flame sensing electrode, fan, or gas valve. Some cost pennies to fix. Some cost hundreds. Guessing at the cause and replacing parts one at a time is the expensive way to find out which one you have. Proper diagnosis first is the cheap way.

A fine spray of water from the bottom-left of a Worcester Greenstar Junior or CDi, but the pressure stays steady. Often a pinhole leak in the supply manifold. A complicated fix that's worth catching.

A small water weep from the top of the boiler with the system pressure slowly dropping. Often a failing automatic air vent (AAV), a known wear part on most modern boilers.

Pressure gauge in the red, boiler locked out and won't fire? You need the filling loop. The three types found in UK homes, which one you have, and how to top up your pressure safely.

A deep sustained trumpet noise from the boiler, with vibration through the wall. Usually a dirty injector on an Ideal Logic. Almost always fixed during a service.

Rust under your boiler, slow pressure loss, faint acidic smell. Common warning signs of a cracked sump on an Ideal Logic, and what your options are.