If you have recently had your boiler serviced or your heating system refilled and suddenly noticed low hot water pressure, you are definitely not alone. This is a common issue for homeowners and it is usually caused by something simple. Before you worry about bigger faults, there are several practical checks you can carry out yourself at home.
Understanding low hot water pressure after service
The phrase low hot water pressure covers a range of symptoms, from weak flow at taps to showers that struggle to maintain temperature. After a routine service or a refill, trapped air, valve positions and system settling can all cause temporary drops in pressure.
Homes across Bordon and nearby areas such as Whitehill, Liphook, Alton and Farnham often experience this after annual boiler maintenance, especially in older properties or those with stored hot water cylinders.
Quick checks you can do now
- Try more than one hot tap to confirm whether the issue is isolated.
- Check whether cold water pressure is normal.
- Check whether the boiler is showing any warning lights or fault codes.
- Listen for gurgling sounds that may indicate trapped air.
Common causes after a system refill
When a system is drained and refilled, it introduces changes in flow and pressure behaviour. Some of the most frequent causes include:
- Air trapped in the hot water pipes – This is especially likely if the pressure dropped immediately after the refill.
- Partially closed service valves – Engineers sometimes isolate valves to carry out service work, and they may not always be fully reopened afterwards.
- Debris disturbed inside the system – Older systems can release small particles when refilled, sometimes temporarily restricting flow.
- Issues with the hot water cylinder – Venting or airlocks around the cylinder can reduce flow at taps.
Checklist: simple homeowner fixes
- Run the hot tap for a few minutes to help move any trapped air.
- Check isolation valves underneath the boiler are fully open.
- If you have a combi boiler, ensure the boiler is firing correctly when hot water is demanded.
- If you have a vented cylinder, listen near the airing cupboard for signs of air movement.
Airlocks and how to spot them
Airlocks are one of the most common reasons for low flow after a refill. You might notice spluttering taps, uneven flow or water that starts and stops. In some properties around the GU35, GU34 and GU9 areas, long pipe runs or pipework changes over the years make airlocks more likely.
While some airlocks clear themselves, you can help the process by running the highest hot tap first and then a lower one. This encourages trapped air to move through the system.
Valve checks and flow restrictions
Partially closed valves can lead to surprisingly large reductions in hot water pressure. Under your boiler there may be several small lever valves. Make sure they sit fully in line with the pipe rather than across it. If you have a system or conventional boiler, also check that any gate valves around the hot water cylinder are fully open.
A partially closed valve elsewhere in the home can also cause problems. If you recently had work done on sinks, radiators or pipework, double-check that nothing has been isolated by accident.
When the issue is inside the boiler
Sometimes the cause is inside the boiler itself. Plate heat exchangers, diverter valves or strainers can become partially blocked, particularly in systems more than ten years old. A service can disturb sediment that then restricts hot water flow. This is not dangerous but will require a Gas Safe engineer to diagnose and correct.
System types and how they affect pressure
Your system design plays a big part in how pressure behaves after a refill:
- Combi boilers – Provide hot water directly from the mains. Any drop in hot water pressure is often linked to flow restrictions or boiler internals.
- System boilers with cylinders – Stored hot water systems can suffer from venting issues, airlocks and issues with the coil inside the cylinder.
- Vented (gravity) systems – Very common in older homes across Bordon and surrounding towns. These are more sensitive to trapped air and ball valve issues in the loft tank.
When to call a professional
If your pressure has remained low for more than 24 hours, none of the simple checks have helped, or you suspect a fault inside the boiler or cylinder, it is best to call a Gas Safe engineer. Persistent issues can indicate deeper problems such as blocked heat exchangers, failing pumps or incorrect valve positions that need expert attention.
Next steps: If your hot water pressure still has not returned to normal, book expert help at https://www.embassygas.com/book