# Tundish overflowing during hot water

**URL:** <https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545>\
**Category:** Heatpump\
**Created:** [26 October 2026 13:21 UTC](https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545 "2026-10-26T13:21:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Godfrey\_Almeida](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/godfrey_almeida/32/25703_2.png) [@Godfrey\_Almeida](https://community.openenergymonitor.org/u/Godfrey_Almeida)\
**Post date:** [26 October 2026 13:21 UTC](https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545/1 "2026-10-26T13:21:37Z")

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Hi

Not related to efficiency here, but has anyone had their pressure topped up by an engineer only for the tundish to then overflow?

thanks

Godfrey

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**Author:** ![arc12](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/arc12/32/20097_2.png) [@arc12](https://community.openenergymonitor.org/u/arc12)\
**Post date:** [26 October 2026 17:06 UTC](https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545/2 "2026-10-26T17:06:58Z")

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I’d call your engineer!

This is not normal and should not be ignored; this is safety equipment!!

Some causes may be easily rectified but there may be a hazardous fault.

One possible cause is low pressure in your expansion vessel and your engineer should be able to check and rectify this easily.

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**Author:** ![glyn.hudson](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/glyn.hudson/32/35003_2.png) [@glyn.hudson](https://community.openenergymonitor.org/u/glyn.hudson)\
**Post date:** [26 October 2026 23:20 UTC](https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545/3 "2026-10-26T23:20:56Z")

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This indicates that the hot water cylinder expansion vessel is not working properly. It will either need to be re-charged with air or most likely replaced. Call an engineer ASAP as it’s a potential safety issue. There’s nothing heat pump specific about it, a boiler engineer will be able to do the job fine.

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**Author:** ![Godfrey\_Almeida](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/godfrey_almeida/32/25703_2.png) [@Godfrey\_Almeida](https://community.openenergymonitor.org/u/Godfrey_Almeida)\
**Post date:** [27 October 2026 06:49 UTC](https://community.openenergymonitor.org/t/tundish-overflowing-during-hot-water/30545/4 "2026-10-27T06:49:59Z")

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Thanks both. Got someone coming on Thursday!