If your heating is working but your hot water turns cold quickly, you’re not alone. Many homeowners in places like Liphook, Bordon, Alton, and surrounding GU35 areas face this issue every year, especially during colder months when demand on the system is higher. This guide explains the likely causes, the safe checks you can do yourself, and when it’s time to call in a professional.
Why your hot water runs cold: common causes
When hot water runs cold unexpectedly, it usually means something is interrupting the heating process within your boiler or cylinder system. The cause depends on whether you have a combi boiler or a system with a hot water cylinder. Both setups can be affected by temperature sensors, flow issues, scale buildup, or diverter valve faults.
Quick checks you can do now
Before calling an engineer, you can safely carry out a few simple checks that often resolve or help diagnose the issue.
- Check your boiler pressure. It should typically sit between 1 and 1.5 bar when cold.
- Ensure the hot water temperature setting hasn’t been turned down accidentally.
- Run the tap slowly to see if the water stays hot longer (high flow can outrun some boilers).
- Restart the boiler to clear temporary faults.
- Check for error codes on the display.
Here’s a quick checklist you can follow:
- Is the boiler pressure normal?
- Do both heating and hot water work briefly?
- Does the boiler flame symbol disappear when the water goes cold?
- Are any nearby taps or showers running simultaneously?
Understanding the science: how your system makes hot water
In combi boiler homes, the boiler heats water on demand. In system and heat-only setups around Liphook and Bordon, a hot water cylinder stores heated water for use throughout the day. If your heating works but your hot water runs cold, it often means the boiler is prioritising the central heating but failing to produce or deliver domestic hot water.
Most likely faults that cause hot water to go cold
Several boiler components regulate hot water temperature. When any of these begin to fail, the system can heat water briefly before cutting out.
- Diverter valve faults: This valve directs hot water to either your heating or your taps. If it sticks, you may get heat but poor hot water performance.
- Blocked plate heat exchanger: Common in hard-water areas such as GU35 and GU34. Limescale slows heat transfer, causing hot water to fade.
- Temperature sensor issues: A faulty sensor can tell the boiler the water is hot when it actually isn’t.
- Low water pressure: Combi boilers need consistent flow to operate correctly. Too little pressure and the burner shuts down.
- Partially blocked filters or pipes: Debris or sludge can restrict hot water pathways.
Why this problem is common in older homes
Many properties around Liphook, Whitehill, Farnham, and Alton still rely on older boilers or cylinders. Over time, scale, sludge, and worn valves become more likely. Systems running on the edge of their capacity—especially smaller combi boilers in larger homes—may struggle to deliver stable hot water when multiple taps or showers are used.
How to narrow down the cause
If your hot water fails only at one outlet, such as a shower, the problem may lie with that fixture’s mixer valve rather than the boiler. But if every tap runs cold after a few minutes, the issue is almost certainly central.
You can try these narrowing steps:
- Compare hot water behaviour from two different taps.
- Check whether the boiler flame indicator stays lit.
- Listen for clicking or cycling noises from the boiler before the water cools.
- Run hot water at a slower flow; if it stays hot, your boiler may be undersized or struggling.
If the heating remains steady but the water does not, the diverter valve or plate heat exchanger is often the culprit. These are repairable issues but require a Gas Safe engineer.
When to call an engineer
If your checks don’t reveal a simple fix, it’s best to book a professional inspection. In towns like Liphook and the wider GU35 area, hard water increases the likelihood of scale, so components can deteriorate faster than expected. A Gas Safe engineer can test sensors, measure flow rates, inspect the diverter valve, clean or replace the plate heat exchanger, and ensure the entire heating and hot water system is performing correctly.
Next steps
If your heating works but your hot water runs cold after a few minutes and the checks above haven’t solved it, you can book a professional diagnosis and repair at https://www.embassygas.com/book