No Heating or Hot Water: A Diagnostic Checklist Before You Call
A few safe checks — pressure, thermostat, fault codes — take minutes and either fix the problem or give the engineer a faster starting point.
Start With What Actually Stopped
Work out whether it's heating, hot water, or both that have stopped, and whether it happened suddenly or has been getting gradually worse. This single detail narrows the likely cause significantly before you even pick up the phone — a combi boiler losing only hot water while heating still works points somewhere different to a total loss of both.
Checks You Can Safely Do Yourself
These take a few minutes and rule out the simplest, most common causes without needing to open the boiler casing at all.
Reading a Fault Code
If your boiler has a digital display and is showing a fault code, note it down exactly — this is genuinely useful diagnostic information, not just a number to be reset away. Different manufacturers use different codes for similar underlying faults, so the exact code and brand together matter. A fault code reference for your specific brand can give you a starting steer on what it typically indicates, though a Gas Safe engineer should always confirm the actual cause on site.
When It's No Longer a DIY Checklist
Some situations move past troubleshooting entirely. A smell of gas, a yellow or orange flame instead of blue, scorch marks near the boiler, or symptoms that could indicate carbon monoxide exposure (headaches, dizziness, especially affecting several people at once) all mean stopping immediately and calling a Gas Safe registered engineer — this is not a checklist situation, it's an emergency one.
Frequently asked questions
What should I check first if I have no heating at all?
Check the pressure gauge is within the normal range, confirm the thermostat is set above room temperature and the programmer has heating scheduled, and check the boiler display for any fault code. These take a few minutes and rule out the most common simple causes.
Is it safe to reset my boiler myself?
Most boilers have a reset button and trying it once is generally safe. If it locks out again immediately, or keeps happening repeatedly, stop resetting it and get it looked at — a fault that needs repeated resets usually needs diagnosis, not repetition.
My hot water works but heating doesn’t (or the reverse) — what does that mean?
On a combi boiler this is a very common pattern and often points to the diverter valve, which switches the boiler between the two functions. It's a well-understood fault an engineer can confirm quickly, not a mystery symptom.