No Hot Water? A Homeowner’s First-Response Checklist

Hello, I’m Tony from Keystone Comfort Solutions. There are few domestic crises quite like that sinking feeling when you turn on the shower on a chilly morning, and the water runs stone cold. The whole household grinds to a halt. It’s stressful, inconvenient, and your first thought is often of a large, unexpected repair bill.

But before you panic, I want you to take a deep breath. As a heating engineer in Epsom for over 30 years, I can tell you that in many cases, a lack of hot water is caused by something surprisingly simple. My promise in this guide is to give you a first-response checklist – a series of calm, safe, and straightforward steps you can take yourself to diagnose the problem. Let’s work through this together, and with a bit of luck, we might just get your comfort restored without you even needing to call for help.

Part 1: The Basic Checks (Your 2-Minute Triage)

Before you even go near the boiler, let’s do a quick triage of the whole house. These simple checks can give us crucial clues about the root cause of the problem.

• Is It Just the Hot Water?
  First, check if the problem is affecting all your hot taps. Try running the hot tap in the kitchen and then in an upstairs bathroom. If one is working but the other isn’t, the issue is likely a plumbing problem (like an airlock in the pipe) rather than a boiler problem. Next, and this is a vital clue, check if your central heating is still working. Go and feel a radiator. If your radiators are getting warm but you have no hot water, it tells us the boiler is firing up, but the heat isn’t being directed to your taps. We’ll come back to why that is.
• Is It a Power Problem?
  It sounds obvious, but you’d be surprised how often this is the culprit. Go to your boiler and look at its display screen. Is it completely blank? If so, it has no power. Before calling an engineer, go to your main fuse box and see if one of the trip switches has flipped to the ‘off’ position. Sometimes, another faulty appliance can trip a circuit that your boiler is also on. If a switch has tripped, try flipping it back on. If it stays on, great! Go and check your boiler. If it trips again immediately, you may have an electrical fault that needs investigating.
• Is It a Gas Supply Problem?
  Your boiler needs gas to create heat. To check if your gas supply is working, go to another gas appliance in your home, like your gas hob. Try to light one of the rings. If it lights and the flame is strong and blue, you know gas is getting to the house, and the problem is with the boiler itself. If the hob won’t light, check if you are on a pre-payment meter that may have run out of credit. If not, it could be an issue with the gas supply in your street, and it’s worth checking with your neighbours or calling your gas supplier.

Part 2: The Boiler Itself (Simple Checks You Can Do Safely)

If you’ve done the basic checks and everything seems okay, it’s time to look at the boiler itself. Don’t worry, we are not going to take anything apart. These are just simple, safe visual checks.

• Check #1: Look for Any Fault or Error Codes
  Most modern boilers are excellent at self-diagnosis. If there’s a problem, they will usually display a specific fault code (e.g., ‘F75’, ‘EA’, ‘F22’). This code is the single most useful piece of information you can have. Write it down carefully. It tells an engineer exactly what the boiler thinks is wrong, which helps us diagnose the problem much faster when you call. You might be tempted to just reset the boiler to clear the code. A word of caution here: it’s okay to try resetting it once. If the boiler fires up and works, brilliant. But if the fault code comes back, do not keep resetting it. The code is there for a reason, and repeatedly ignoring it can sometimes cause a bigger, more expensive problem.
• Check #2: Check the Boiler’s Pressure Gauge
  Look for a small dial on the front of your boiler, usually with green and red sections. This shows the pressure of the water within your central heating system. For the boiler to work correctly, this needle should be in the green zone, typically between 1 and 1.5 bar. If the needle has dropped into the red (below 0.5 bar), the boiler’s safety systems will shut it down to protect it from damage, which means no heating and no hot water. Low pressure is a very common issue, and you can find a link to our simple, safe guide on how to re-pressurise your boiler system here.
• Check #3: Check Your Thermostat and Timer Settings
  Sometimes, the solution is embarrassingly simple! Go and check your central heating programmer or timer. Has the hot water accidentally been switched to the ‘off’ setting? Have the timings been changed? If you have a separate hot water tank thermostat, check that the temperature hasn’t been turned right down. And if you have a modern wireless room thermostat, a common culprit is the batteries running out. If the screen is blank or flashing a low battery symbol, replacing the batteries might be all you need to do to get things working again.

Part 3: Understanding the Cause (Why Has This Happened?)

If you’ve been through the checks, you might have a better idea of the cause. Here’s what the clues usually point to from an engineer’s perspective.

• If You Have Heating but No Hot Water (The Common Culprit)
  This is a classic symptom, especially in combi boilers. It almost always points to a problem with a component called the ‘diverter valve’. This valve is like a set of traffic lights inside your boiler. When you’re not using hot water, it directs the heat to your radiators. When you turn on a hot tap, it’s supposed to swing over and direct all the heat to your water supply. These valves can get worn out or stuck, meaning they stay in the ‘heating’ position even when you want hot water. This requires a professional to free up or replace the valve.
• If You Have No Heating AND No Hot Water
  This suggests a more central boiler failure. The boiler isn’t firing up at all. Following the checks above, this could be due to a lack of power, no gas, low pressure, or a fault with a critical component like the fan, the pump, or the main circuit board (PCB). This will definitely require a professional diagnosis.
• If Your Hot Water is Only Lukewarm
  If the water is getting warm but not properly hot, or it runs hot for a minute then goes cold, this often points to a partially blocked plate heat exchanger. This is the part that transfers the heat to your tap water. Over time, it can get clogged up with limescale and sludge, especially in hard water areas like ours in Surrey. This restricts the heat transfer, resulting in disappointing, lukewarm showers.

When to Stop and Call a Professional Engineer

You have been brilliant and done all the safe checks you can. It’s now time to stop and call a professional if:

• You’ve tried all the simple checks above and nothing has worked.
• You suspect a gas leak. If you can smell gas, do not touch any electrical switches. Immediately open all windows, turn the gas off at the meter, and call the National Gas Emergency Service and then an engineer like myself from outside the property.
• The boiler is making loud banging, whirring, or gurgling noises.
• You can see water actively leaking or dripping from the main boiler casing.

How We Handle a “No Hot Water” Emergency Call at Keystone

When you call us in a panic, we know our first job is to be a calm and reassuring voice. To help us help you faster, try to have the following information to hand: the make and model of your boiler (e.g., “a Worcester Bosch Greenstar 28i”) and the fault code if one is showing. This information allows me to start diagnosing the problem before I even get to your home in Tadworth or Coulsdon. Our goal is always to get your comfort restored as quickly and efficiently as possible, with an honest diagnosis and clear, upfront pricing before we start any repair work.

Your Quick-Reference “No Hot Water” Checklist

1. Check Power: Is the boiler display on? Check the fuse box.
2. Check Gas: Is your gas hob working?
3. Check Pressure: Is the boiler pressure gauge in the green zone (1-1.5 bar)?
4. Check Code: Is there a fault code on the display?
5. Check Settings: Are the timer and thermostat set correctly?

Frequently Asked Questions from Surrey Neighbours in a Cold Shower

Why does my hot water run out so quickly?

If you have a combi boiler, this can be a sign of a partially blocked plate heat exchanger. If you have a conventional system with a hot water cylinder, it could be an issue with the cylinder’s thermostat or that the cylinder itself is simply too small for your family’s needs.

How long does it take to fix a diverter valve?

For an experienced engineer who carries common parts on their van, replacing a diverter valve on a popular boiler model is usually a job that can be completed in around an hour to an hour and a half.

Is an emergency with no hot water call-out is expensive?

Most engineers will have a standard call-out fee which covers the first hour of diagnosis and work. Any parts required will then be an additional cost. Here at Keystone, we are always transparent about our pricing, so you’ll know the full cost before we proceed with a repair.

Could this be a problem with my hot water cylinder instead of the boiler?

Yes, absolutely. If you have a “system” or “regular” boiler (not a combi), the problem could be with the cylinder. It could be an issue with the motorised valves that control it, or the cylinder thermostat. This is something we would check as part of our diagnosis.