Pump troubleshooting
My hot water pressure is low but the cold is fine
If your cold water is strong but the hot runs weak, you can rule out your main supply straight away, water reaches the house fine, so something in the hot-water path is holding it back. Here’s where to look.
Why hot-only points to the hot path
Your hot and cold split after the water enters the house: cold goes straight to the taps, hot goes via your hot water system. If only the hot is weak, the restriction is somewhere on that hot journey, so that’s where to focus.
The usual causes
- A failing or partly-blocked tempering (mixing) valve, the safety valve that blends hot to a safe temperature. A very common culprit.
- Sediment or scale build-up in the hot water system or its outlet.
- A partly-closed isolation valve on the hot line.
- On some systems, a pressure-limiting valve set low.
What to check
- Confirm it really is hot-only, test the hot tap at a couple of outlets.
- Check the isolation valves on the hot water unit are fully open.
- If your system has a tempering valve (most do), it’s the most common cause of gradual hot-only pressure loss and can be replaced by a plumber.
- An older hot water system can silt up internally; a plumber can advise whether flushing will help or it’s nearing replacement.
Safety: Tempering valves and hot water systems are plumbing, and often regulated, work. If the basics are open and it’s still weak, have a plumber test the tempering valve and the system.
Common questions
What’s a tempering valve?
A safety valve that blends hot water down to a safe temperature (around 50 degrees at the tap) to prevent scalding. When it starts to fail it commonly restricts hot-water flow, which shows up as low hot pressure. Replacing it’s a standard plumber job.
Would a pressure pump fix low hot pressure?
Only if your whole-house pressure is low to begin with. If your cold is strong and only the hot is weak, a booster won’t help, the restriction is in the hot path, so fix that instead.