No hot water. Five checks before you call.

Where do the two-minute checks start?

In order, cheapest suspect first:

1. Pressure gauge. Below 1 bar and most combis refuse to play. Top up through the filling loop — the manual shows how — and close the loop after.
2. Controls. Thermostat nudged down, timer on the wrong schedule, clock still an hour out from the last time change. Someone "just adjusting" it is the classic culprit.
3. Power. A tripped switch or breaker at the consumer unit kills a boiler as dead as any fault. Check the boiler's fused spur hasn't been switched off too.
4. Condensate pipe. In a hard frost, the small white pipe outside freezes and the boiler shuts down to protect itself. Warm water — never boiling — poured along it usually frees things.
5. One reset. Once. Photograph any error code first, because the reset wipes it and the code tells the plumber where to look.

Heating fine, taps freezing?

That split — radiators hot, hot tap cold, or the other way round — is a useful clue, not a mystery. On a combi it usually points at the diverter valve, the part that decides whether the boiler heats your radiators or your tap water. When it sticks, one side wins and the other goes cold.

It's a common wear-and-tear failure and there's no dial to twiddle for it. What you can do is say those exact words on the phone — "heating works, taps run cold" — and the plumber arrives already halfway to a diagnosis.

Cylinder in the cupboard instead of a combi?

Different animal, different checks. If your hot water comes from a tank — common in older Ayr homes that have never switched to a combi — look for the immersion heater switch, usually on the wall near the cylinder or in the airing cupboard. Check it's on, then check its fuse or breaker at the consumer unit.

If the cylinder is heated by the boiler, make sure the programmer actually has hot water scheduled on — it's separate from heating on most setups. A cylinder that's lukewarm at the top and cold below has probably just been emptied by three showers in a row; give it time to recover before declaring a fault. Cold all day with everything switched on points at a failed element, thermostat or motorised valve — professional territory.

Tap coughing and spitting instead of running?

Spluttering, banging, air where water should be — that's an airlock, and it loves appearing just after the water has been off or work has been done on the system. Sometimes it clears itself if you leave the tap running gently for a few minutes. Sometimes it digs in and needs pushing through, which a plumber can do quickly.

Either way it's worth mentioning on the call, along with anything else that changed recently — a new appliance, a repair, a stopcock that got shut. Plumbing faults rarely appear from nowhere; the story usually matters.

Thinking about opening the casing?

Don't. Everything on the outside of the boiler — gauge, filling loop, controls, reset, condensate pipe — is yours to check. Everything behind the casing belongs to a Gas Safe registered engineer, by law and by common sense. There is no YouTube video worth a gas leak.

And if you smell gas at any point, stop reading, stop checking. Everyone out, no switches, no flames, and call the National Gas Emergency Service on 0800 111 999 from outside. The hot water can wait. Gas doesn't.