No Hot Water? Common Causes & Quick Fixes
Waking up to no hot water is one of the most frustrating plumbing problems homeowners face—especially during winter months across Crawley, Horsham, and West Sussex. Whether your boiler isn't producing hot water, your taps are running cold, or your central heating works but there's no hot water, this comprehensive guide will help you diagnose the problem.
At Mend Your Home, we respond to hundreds of "no hot water" calls every year across Crawley, Horsham, Redhill, Reigate, Horley, East Grinstead, Haywards Heath, Burgess Hill, Brighton, Epsom, and throughout West Sussex and Surrey. Many of these issues have simple solutions you can try yourself before calling a professional.
In this guide, we'll cover the most common reasons for no hot water, step-by-step troubleshooting, and when you need to call an emergency plumber.
Quick Diagnosis: Type of Hot Water Problem
First, identify which type of problem you're experiencing:
Complete Loss of Hot Water
No hot water from any tap or shower. Central heating may or may not be working.
Most common cause: Boiler fault, pilot light out, or power/gas supply issue
Lukewarm Water Only
Water is warm but not hot enough. Temperature seems lower than normal.
Most common cause: Thermostat setting, diverter valve, or heating element issue
Hot Water Runs Out Quickly
Hot water starts fine but goes cold after a few minutes.
Most common cause: Cylinder issue, boiler cycling, or insufficient boiler capacity
Heating Works But No Hot Water
Central heating radiators get hot, but taps and showers are cold.
Most common cause: Diverter valve fault, motorized valve, or programmer issue
Common Causes of No Hot Water (By Boiler Type)
Combi Boilers (Most Common in UK)
Combi boilers heat water on demand and are the most popular system across Crawley and West Sussex. Common hot water issues include:
If pressure drops below 1 bar, many combis won't heat water. Check the pressure gauge.
Switches between heating and hot water. When stuck, you get one but not the other.
Detects when you turn on a hot tap. If broken, boiler doesn't know to heat water.
Scale buildup restricts water flow, especially in hard water areas like parts of West Sussex.
In winter, the external pipe can freeze, causing the boiler to shut down completely.
System Boilers (With Hot Water Cylinder)
System boilers store hot water in a cylinder. Issues can be with the boiler, cylinder, or controls:
Controls hot water flow to cylinder. If stuck closed, no hot water gets heated.
Tells boiler when water is hot enough. If faulty, water doesn't heat properly.
If hot water isn't scheduled "on," the boiler won't heat it even if it's working fine.
Air trapped in pipes prevents hot water circulating to the cylinder properly.
If your backup immersion also fails, you have no way to heat water at all.
Step-by-Step Troubleshooting Guide
Try these checks in order before calling a plumber. Many "no hot water" problems have simple fixes:
Step 1: Check the Basics
- Power supply: Is the boiler switched on? Check the switch near the boiler and the fuse box.
- Gas supply: Is the gas supply on? Check other gas appliances work.
- Pilot light: For older boilers, check if the pilot light is lit (small blue flame visible through window).
- Error codes: Check the boiler display for error codes and note them down.
- Timer settings: Ensure hot water is scheduled "on" on your programmer/thermostat.
Step 2: Check Boiler Pressure
Low pressure is the #1 cause of no hot water in combi boilers:
- Find the pressure gauge: Usually on the front of the boiler, shows 0-4 bar.
- Correct pressure: Should be between 1-1.5 bar when system is cold.
- Too low? You need to repressurise the system (see your boiler manual or call us).
- Too high? Over 2.5 bar when cold may indicate a fault requiring professional attention.
Step 3: Check Temperature Settings
- Hot water thermostat: Some boilers have a separate control for hot water temperature. Try turning it up.
- Should be: 50-60°C for hot water (combi boilers often show this as a separate dial or setting).
- Wait 10 minutes: After adjusting, give the boiler time to heat up the water.
Step 4: Check for Frozen Pipes (Winter Only)
In cold weather across West Sussex, condensate pipes can freeze:
- Location: White plastic pipe coming out of boiler, usually runs to outside drain.
- Signs of freezing: Boiler making gurgling sounds, error code showing, no hot water or heating.
- Thawing method: Pour warm (not boiling) water slowly over the frozen section of pipe.
- Reset boiler: Once thawed, reset your boiler according to manual.
Step 5: Try Resetting the Boiler
Sometimes a simple reset fixes temporary glitches:
- Find the reset button: Usually on the front panel or control unit.
- Press and hold: For 3-5 seconds (check your boiler manual for exact method).
- Wait: Give the boiler 2-3 minutes to go through its startup sequence.
- Test: Try running hot water again.
- Note: If you need to reset repeatedly, there's an underlying fault that needs fixing.
Still No Hot Water? We Can Help
Gas Safe registered engineers across Crawley, Horsham, and West Sussex
Open 8am-7pm, 7 days a week
When to Call a Professional Plumber
Call a Gas Safe registered engineer if you experience any of these:
Gas Smell
Any smell of gas is dangerous. Turn off gas supply, ventilate, evacuate, call National Gas Emergency: 0800 111 999
Persistent Error Codes
Error codes that don't clear after reset indicate internal faults requiring professional diagnosis
Water Leaks
Leaking from boiler, pipes, or radiators. Turn off water supply and call emergency plumber
Strange Noises
Banging, whistling, or gurgling sounds from boiler indicate internal problems
Multiple Attempts Failed
If basic checks don't fix the problem, you need professional diagnosis and repair
Old Boiler (15+ years)
Older boilers often need professional service. May be more cost-effective to replace
Preventing "No Hot Water" Problems
Regular maintenance prevents most hot water issues. Here's what homeowners across Crawley and West Sussex should do:
Annual Maintenance Checklist:
- Annual boiler service - Essential for safety and efficiency (from £105 with Mend Your Home)
- Check pressure monthly - Top up if it drops below 1 bar
- Bleed radiators yearly - Removes air that can affect hot water production
- Insulate pipes - Prevents freezing in winter months
- Test hot water regularly - Don't wait for cold weather to discover problems
- Know your system - Keep boiler manual handy, understand basic controls
- Address issues quickly - Small problems become expensive emergencies if ignored
- Consider a service plan - Annual servicing + priority emergency call-outs
FAQs About No Hot Water
Why do I have heating but no hot water?
Most commonly, this is a diverter valve fault in combi boilers, or a motorized valve/programmer issue in system boilers. The boiler works fine but isn't directing heat to your hot water system. Requires professional repair.
How long does it take for hot water to come back?
Combi boilers heat water instantly once working. System boilers need 30-60 minutes to heat a full cylinder. If you've just repressuried or reset your boiler, wait 5-10 minutes then test.
Can I shower if I have no hot water from the boiler?
If you have an electric shower fed directly from mains water, it will still work even if your boiler has failed. However, mixer showers that blend hot and cold water won't work properly without hot water supply.
Is no hot water an emergency?
While not usually life-threatening, no hot water in winter can be urgent, especially with young children, elderly residents, or health conditions. It's also a hygiene issue. We prioritize hot water emergencies during business hours.
How much does it cost to fix no hot water?
Costs vary widely depending on the cause. Simple fixes like repressuriing (DIY: free) or replacing a thermostat are relatively inexpensive. Major component failures like heat exchangers or complete boiler replacement cost more. We provide clear quotes before starting work.