If you are getting hot water at your boiler or one tap, but cold water at others, the good news is that the issue is often small and fixable. Many homeowners across Bordon, Whitehill, Liphook, Alton, and Farnham run into this problem, and a few careful checks can help you narrow down the cause.
Understanding the situation with boiler hot water cold taps
When some taps run cold while your boiler is clearly producing hot water, the issue is usually localised. That means it is often linked to valves, filters, diverters, or flow issues rather than a boiler breakdown.
The steps below will help you pin down what is happening before calling in a Gas Safe engineer.
Quick checks you can do now
- Ensure your hot water settings are correct on the boiler or programmer.
- Confirm that only certain taps are cold, not the whole house.
- Try both hot and cold sides on mixer taps separately.
- Check whether the problem affects upstairs, downstairs or both.
- Open another hot tap to see if the boiler fires up.
If you are in GU35, GU34 or GU9, these are the same steps any local engineer will begin with.
Check 1: Are your boiler settings correct?
This is a simple place to start. On combi boilers, the hot water temperature control and sometimes the flow setting influence how quickly hot water reaches taps. If the temperature dial has been knocked or turned down, a tap may feel cold even though the boiler is generating some warmth.
- Check the hot water temperature dial.
- Make sure the boiler is not in ‘eco’ mode if you prefer higher flow temperatures.
- Check the programmer or smart controls are not turning hot water off.
If the boiler fails to fire when you open a hot tap, the issue may be with flow recognition or a sensor, but if it fires normally, proceed to the next steps.
Check 2: Mixer tap faults and airlocks
Many homeowners assume a boiler issue when the problem is actually a faulty mixer tap or trapped air in pipework. A mixer tap cartridge can fail on one side, allowing only cold water through.
Quick test:
- Turn the mixer fully to hot.
- Check whether the boiler activates.
- Try a different hot tap to compare.
If one mixer tap runs cold but another tap in the house runs normally, the fault is likely at the tap, not the boiler.
Airlocks are less common on mains-fed systems but can still affect isolated fixtures. If the issue began suddenly after plumbing work, this is worth considering.
Check 3: Understanding and testing the diverter valve
The diverter valve is essential in combi boilers. It directs heat either to the central heating system or to your hot water taps. When it sticks or becomes partially faulty, it might send heat mainly to radiators even when a hot tap is opened, leaving you with cold taps.
Signs your diverter valve may not be behaving correctly:
- Radiators warm up when a hot tap is opened.
- Hot water is available only at one tap.
- The boiler fires but hot water never reaches certain outlets.
Homeowner checks you can safely make:
- Turn off your heating and then open a hot tap. Check whether the boiler fires solely for hot water.
- If radiators start to warm during this test, the diverter valve may be stuck.
Although repairing a diverter valve is a Gas Safe task, identifying symptoms can save diagnostic time.
Check 4: Hot water pump or flow issues
Not all boilers use a separate hot water pump, but system and heat-only boilers may rely on one, especially when paired with an unvented cylinder. If your cylinder produces hot water but upstairs taps run cold, the circulation pump could be struggling.
Things to look for:
- A pump running unusually quietly or loudly.
- Pipes near the cylinder feeling hot on one side and cool on the other.
- Cold taps that improve temporarily after using a high-flow tap elsewhere.
Some circulation problems show up only at the furthest taps from the cylinder or boiler. In areas like Bordon and Liphook where older pipework is common, sludge buildup can make this more noticeable.
Check 5: Flow restrictors, filters and partially blocked pipes
Modern taps and showers often include flow restrictors. If these become blocked, they can reduce flow so much that the boiler does not recognise a hot water request.
Simple homeowner-friendly checks:
- Unscrew the tap aerator and clean any grit or limescale.
- Check if the tap runs properly with the aerator removed.
- Inspect shower hoses for kinks or blockages.
Limescale buildup is common in hard-water areas, including around Alton and Farnham. Clearing visible deposits can quickly restore flow.
Check 6: Cylinder and system-specific considerations
If you have a hot water cylinder rather than a combi boiler, different faults can cause hot and cold imbalances.
Key cylinder-related things to consider:
- Has the cylinder reached full temperature? (Check the thermostat.)
- Are the motorised valves opening correctly?
- Is the hot water venting or gurgling, suggesting circulation issues?
Older vented systems in parts of Whitehill and GU35 areas sometimes suffer from loft tank issues, including stuck ball valves or low water levels, leading to inconsistent flow at individual taps.
Check 7: Pressure issues and flow sensors
Combi boilers rely on a minimum flow rate to activate hot water mode. If a tap’s flow is too weak, the boiler may simply not ‘see’ the demand.
Check the following:
- Is your cold water pressure normal?
- Does the affected tap have noticeably poor flow?
- Does the boiler fire at one tap but not another?
If the boiler fires for some taps but not others, the issue is highly likely to be tap-side, not within the boiler.
Checklist: When to call an engineer
- You suspect a diverter valve fault.
- Your pump makes unusual noises or feels excessively hot.
- The problem affects multiple taps with no obvious blockage.
- Your boiler fails to fire on hot water demand.
- You have an unvented cylinder with uneven temperatures.
Preventing future isolated cold tap issues
A little routine care can minimise the risk of hot water imbalance:
- Clean tap aerators every few months.
- Have your boiler serviced annually.
- Flush debris from pipes after any plumbing work.
- Keep boiler settings consistent and note any changes.
Homes in Bordon and nearby areas like Liphook or Alton often have older pipework that benefits from good maintenance and regular checks.
Next steps
If you have worked through these steps and still have hot water at the boiler but cold taps elsewhere, our Gas Safe team can help. Contact us at (01420) 558993.