Why Your Heating Isn't Working When Hot Water Is
It can be a peculiar situation: your taps deliver lovely hot water, but the radiators stubbornly refuse to warm up. This common household puzzle, where your hot water is working but the heating is not, often leaves people scratching their heads. Fortunately, it usually means your boiler itself is still functional, producing heat, but something is preventing that heat from circulating through your radiators. It’s a sign that the core of your heating system is likely sound, but a specific component or setting related to the heating circuit is misbehaving.
Understanding the distinction between the hot water and heating circuits is key. Your boiler typically has two main jobs: providing instant hot water for taps and showers, and heating the water that circulates through your radiators. When only one of these functions is failing, it isolates the problem to a particular part of the system. This common issue, 'hot water working heating not', often boils down to a few specific culprits, making it a scenario where a bit of homeowner investigation can sometimes save a call-out fee.
- Hot water working while heating fails points to a specific heating circuit issue.
- Your boiler likely functions but a part is preventing heat circulation.
- This problem often allows for some homeowner checks before professional help.
- Separating hot water and heating circuit functions helps diagnose the fault.
Common Causes of No Heating, Just Hot Water
Several factors can lead to your heating failing while hot water remains available. One of the most frequent is a problem with your central heating pump. This pump is responsible for circulating hot water from the boiler to your radiators. If it's faulty, stuck, or not receiving power, the water won't move, leaving your radiators cold even though the boiler is hot. Another common issue is a faulty diverter valve. This valve directs hot water either to your taps or to your heating system. If it's stuck in the 'hot water' position, it won't send heat to the radiators.
Pressure drops within the heating system can also cause this. Many modern boilers have safety features that will shut down the heating circuit if the water pressure falls too low, often below 1 bar. You might notice this if the pressure gauge on your boiler is showing a low reading. Less common, but still possible, are issues with airlocks in the system, or a problem with a motorised valve controlling the flow to your radiators. These valves might fail to open, preventing water circulation.
The most common reason for hot water working but heating not is often a fault with the central heating pump or a stuck diverter valve.
Sometimes, the problem isn't with the boiler itself but with the controls. A malfunctioning thermostat or a faulty programmer could be telling the boiler not to fire up the heating, even if it's trying to provide hot water. These controls are like the brain of your heating system, and if they are confused, they can lead to peculiar behaviour like this.
What You Can Check Before Calling a Professional
Before you reach for the phone to book a heating engineer for your 'hot water working heating not' dilemma, there are a few straightforward checks you can perform yourself. These basic troubleshooting steps can sometimes resolve the issue or at least provide valuable information for the engineer, potentially saving you time and money. Always ensure you know where your boiler's isolation switch is and how to safely turn off your boiler before attempting any checks that involve touching components.
Start with the obvious: check your thermostat. Ensure it's set to 'heating' or 'auto' mode and that the desired temperature is higher than the current room temperature. Sometimes, a simple programming error or a dead battery in a wireless thermostat can cause the heating to stay off. Next, inspect your boiler's pressure gauge. If the pressure is below 1 bar (or whatever the manufacturer recommends on the boiler's casing or manual), you may need to top up the system. Look for a filling loop, usually a small hose or lever near the boiler, and carefully follow your boiler's manual instructions to increase the pressure. Do not over-pressurise the system.
Carefully check if your boiler has a specific 'winter' or 'heating' mode that might have been accidentally switched off.
Investigating Boiler Controls and Indicators
Take a look at your boiler's display panel. Many modern boilers will show error codes or warning lights if they detect a fault. Consult your boiler's manual to decipher these codes. For example, a 'F' code might indicate a fan issue, while a 'P' code could relate to pump problems. If you see any such codes related to the heating circuit, it's a strong indicator of the fault's nature. Also, listen to your boiler when it should be calling for heat. Do you hear the pump trying to run? Is there any unusual noise?
If you have a system with motorised valves (often found in larger homes with a hot water tank), you might be able to check if they are open. These valves usually have an actuator on top and may have a manual override lever. Sometimes, gently flicking this lever to the 'manual' or 'open' position can get the heating started, at least temporarily. This suggests the valve itself or its electrical control is the problem. If you have a combi boiler, you won't have these separate valves for hot water and heating; the diverter valve inside the boiler is the usual suspect.
The key is to determine if the boiler is attempting to heat water but it's not circulating, or if it's not even attempting to start the heating cycle. This distinction significantly narrows down the potential causes and guides your next steps, whether that's attempting a minor adjustment or calling in a qualified professional.
When to Call a Gas Safe Registered Engineer
If you've gone through the basic checks and your heating still isn't working, or if you're uncomfortable performing any of these steps, it's time to call in a Gas Safe registered engineer. Attempting repairs beyond your comfort level, especially on gas appliances, can be dangerous and may void your boiler's warranty. A professional has the tools, knowledge, and certification to safely diagnose and fix complex issues within your heating system.
Specifically, if you suspect a fault with the boiler's internal components such as the diverter valve, pump, printed circuit board (PCB), or pressure sensor, only a qualified engineer should handle it. Issues related to the boiler's burner, ignition system, or gas supply also require expert attention. For 'hot water working heating not' problems, an engineer can perform tests on the pump, valves, and electrical controls to pinpoint the exact cause. They can also accurately repressurise the system if needed, or bleed air from radiators if that's suspected to be the issue.
Making the Most of Your Engineer Visit
When you book an engineer, be prepared to describe the problem clearly. Mention that you have hot water but no heating, and explain any checks you've already made and any error codes you observed on the boiler. This information helps them arrive with the right parts or a better understanding of the potential fault. For instance, if you've identified a low-pressure reading, letting them know in advance can be helpful. If your boiler is still under warranty, ensure you contact the manufacturer or an approved service provider first, as using an unapproved engineer could invalidate the warranty terms.
The peace of mind that comes with a professionally diagnosed and repaired heating system is invaluable, especially during colder months. While it might seem costly, addressing the issue promptly can prevent further damage and ensure your home remains comfortable and warm. Always compare quotes if possible, but prioritise safety and reliability when choosing an engineer.