There’s a particular kind of dread that comes with turning the tap in January and getting nothing but cold. Or coming downstairs to find the central heating not working, radiators stone cold, and a boiler that’s decided to give up overnight.
The good news: a lot of the time, the fault is something you can identify in ten minutes, and sometimes fix yourself. The rest of the time, knowing what is wrong before you pick up the phone saves you a wasted appointment.
This guide from our Gas Safe heating engineers at The Edinburgh Boiler Company goes through it question by question. Start with what your broken boiler is actually doing, not what you think is wrong.
What should I check first if I have no hot water or central heating?
Three things, before anything else:
- Is there a fault code on the display? Write it down. It’s the single most useful piece of information you can give an engineer.
- What does the pressure gauge read? Most boilers want between 1 and 1.5 bar when the system is cold.
- Do your other gas appliances work? If the hob won’t light either, the problem is your gas supply, not your boiler.
Then find your symptom below.
Why do I have no hot water when the central heating is working?
This is the classic combi boiler fault, and nine times out of ten it points to the diverter valve.
Your combi has one heat exchanger doing two jobs. When you run a tap, the diverter valve switches the flow from the radiators over to your hot water. When it sticks — usually through wear or debris in the system — it stays stuck on heating. Radiators lovely, showers freezing.
Are there other signs of a faulty diverter valve?
Yes. Water that’s only ever lukewarm, or hot water that only appears when the heating is on, both point the same way.
Can I fix a diverter valve myself?
No. It’s a component replacement inside the boiler and it’s a Gas Safe job. It’s a common repair, though, and usually a straightforward one.
Why is my central heating not working when the hot water is fine?
Your boiler is clearly firing, so work through the controls first.
Could it be the programmer or timer?
Often. Power cuts reset these constantly. Check the time and date are right — a clock stuck at the wrong hour means the heating is coming on at 3am and nobody’s noticed.
Could it be the room thermostat?
Wireless thermostats run on batteries and they die silently. Swap them, then check the target temperature is actually above the current room temperature.
Could it be the radiator valves?
Turn a thermostatic radiator valve up. If nothing happens, the pin under the head may be seized — a very common fault after a summer of sitting untouched.
What if the controls all check out?
If everything above is fine and the central heating still isn’t working, you’re likely looking at a seized pump or a failed motorised valve. That’s an engineer’s job.
Why do I have no hot water and no central heating at all?
Work down this list in order.
Is it a power problem?
Is the boiler display lit? Check the fused spur next to the boiler (usually a 3A fuse) and your consumer unit for a tripped breaker or RCD.
Is it a gas problem?
If you’re on a prepayment meter, check your credit — running out cuts the boiler off before you notice anything else. If other gas appliances are dead too, contact your supplier.
Is it low pressure?
If the gauge is below 1 bar, the boiler will lock out to protect itself. See the pressure section below.
Should I just keep resetting the boiler?
No. Modern boilers shut down and display a code rather than run with a fault. One reset is fine. If it locks out again, stop — repeated resets don’t fix anything and can turn a small fault into an expensive one.
Could a frozen condensate pipe be why my central heating is not working?
In a Scottish winter, a frozen condensate pipe is usually the answer of the lot. If your boiler has stopped dead during a cold snap, is making a gurgling or bubbling noise, and is showing a fault code, this is almost certainly it.
Every condensing boiler produces slightly acidic waste water, which drains away through a plastic pipe — usually white or grey, roughly the thickness of a waste pipe, running through an external wall to a drain or soakaway. When temperatures drop below freezing, the water inside turns to ice and blocks it. The boiler detects the blockage and shuts itself off, leaving you with no hot water or heating.
How do I thaw a frozen condensate pipe?
- Find the outside end of the pipe and feel for the blockage — usually at a bend, an elbow, or the open end.
- Pour warm water over it. Not boiling. Boiling water can crack the plastic and, on a freezing morning, refreeze into a worse blockage. Hot water from the tap is ideal. A hot water bottle or wheat bag held against the pipe works well too.
- Once water is running through, reset the boiler.
Don’t attempt this if the pipe runs somewhere you’d need a ladder to reach. It isn’t worth a fall.
How do I stop it freezing again?
Lag the external section with weatherproof pipe insulation, or have the pipe rerouted internally or upsized. If yours freezes every winter, the installation isn’t right for the climate it’s in — worth fixing properly rather than thawing every January.
Why does low boiler pressure leave me with no hot water or heating?
Below roughly 1 bar, most boilers simply won’t fire.
How do I repressurise my boiler?
Find the filling loop — usually a braided silver hose with a valve at each end, or an internal keyed filling link on newer boilers. Open both valves slowly, watch the gauge, and close them as soon as you reach 1.5 bar. Overshooting isn’t dangerous, but it’ll push water out through the pressure relief valve and you’ll be back where you started.
Why does my boiler keep losing pressure?
That’s the more important question. Pressure loss isn’t normal. If you’re topping up every few weeks, you have one of three things:
- A leak on the system — check under radiators, around pipework and beneath the boiler for damp patches or rust marks.
- A failed expansion vessel, which is a routine repair.
- A weeping pressure relief valve, which often shows up as water dripping from a small copper pipe outside.
If the gauge is sitting high instead — up near 2.5 or 3 bar — that needs looking at too, and it usually points to the expansion vessel as well.
Why are my radiators cold when the boiler is working?
- Cold at the top, warm at the bottom: trapped air. Bleed the radiator with a key, then check your pressure afterwards — bleeding drops it.
- Cold at the bottom, warm at the top: sludge and corrosion debris settling. That’s a power flush or system clean, worth doing before it takes out your pump.
- One radiator cold, the rest fine: almost always a seized TRV pin.
- Upstairs hot, downstairs cold (or the reverse): the system needs balancing.
When should I stop troubleshooting and call for help?
Some things aren’t a diagnosis exercise.
What if I can smell gas?
Don’t touch light switches or anything electrical. Don’t use your phone indoors. Open windows and doors, turn the gas off at the meter if you can reach it safely, get everyone outside, and call the National Gas Emergency Service on 0800 111 999 — free, 24 hours a day, and it covers Scotland.
What if my carbon monoxide alarm sounds?
Same response. Get out, get fresh air, call 0800 111 999. If anyone has a headache, nausea or dizziness that eases when they leave the house, tell your GP or NHS 24 on 111.
What other warning signs mean I should switch the boiler off?
Yellow or orange flames instead of crisp blue, or black sooty staining around the casing — turn it off and don’t use it. Same if water is leaking from the boiler: switch it off, isolate the water supply to it, and get an engineer out, because a leak inside the casing corrodes components fast.
Never open your boiler casing and never attempt a repair inside it. Working on gas appliances without Gas Safe registration is illegal, and it invalidates your insurance.
Should I repair or replace a boiler that keeps leaving me with no hot water?
If your boiler is under eight years old and has been serviced regularly, a repair is almost always the sensible answer. Parts are available, it’s likely still efficient, and there may be warranty left on it.
Once a boiler passes eight years old, the maths changes. Parts get harder to source and more expensive. Efficiency has usually drifted well below what it was on installation day, so you’re paying more per unit of heat than you need to. And one repair tends to be followed by another — you end up spending a few hundred pounds a year keeping something alive that was going to need replacing anyway.
Our rule of thumb: if the repair costs a significant share of a new installation and the boiler is over eight years old, replacing it is usually the better decision. A new A-rated boiler with a long manufacturer’s warranty removes the annual gamble entirely.
Not sure which side of that line you’re on? Ask us. We’ll tell you honestly, including when a repair is the right call.
How do I stop being left with no hot water or central heating again?
Most of the faults above give warning signs long before they leave you cold. An annual service catches falling pressure, a tired pump, a diverter valve on its way out, and a condensate pipe that’s going to freeze the moment the temperature drops.
It’s also the only way to be certain your boiler is burning safely. And if you’re a landlord, an annual Gas Safety Record is a legal requirement, not an option.
The best time to book is early autumn — before the first cold snap, when every engineer in Scotland is fully booked.
Who can fix no hot water or central heating in Edinburgh?
If you’ve worked through this and you need a Gas Safe engineer, we can help.
- Boiler repairs — fast diagnosis and repair across Edinburgh and the Lothians, by engineers who work on these systems every day.
- Boiler servicing — a full annual service that keeps your boiler safe, efficient and far less likely to fail when you need it most.
- New boiler installation — if your boiler is over eight years old, unreliable or beyond economic repair, we’ll talk you through your options and install a new one with a long warranty behind it.
Get in touch with The Edinburgh Boiler Company and we’ll get your hot water and central heating back on.
