DIY Doctor

Unvented Hot Water system overflowing?

Postby hubenstein » Fri Dec 03, 2010 8:00 am

My unvented system is overflowing, dripping, and the Tundish is so scaly the water is dripping on to the floor. We noticed it because the ceiling downstairs developed a wet patch.

My own diagnosis is that there seems to be two issues. 1. it is overflowing and 2. the tundish is blocked.

Will it be ok to use descaler on the tundish pipe to get that flowing to at least relieve the symptoms while I get someone to look at why it is overflowing in the first place.

Where does the overflow go?
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Simply Build It

Postby Slater » Sat Dec 11, 2010 9:32 am


I also have a tundish overflowing on my 3 year old system. Not making the surrounding area wet and not scaled up.... yet. There are a couple of red valves but I don't understand the system.

Would appreciate advice on how to stop the flow.

Any ideas could help 2 of us.

Thanks in advance.

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Postby matt00 » Sun Dec 12, 2010 9:52 am

Slater- the red valves are probably pressure relief valves, designed to protect your system from a dangerous increase in pressure or temperature and these are letting by and causing the water to flow into the tundish. Check your pressure and make sure its not too high (3 Bar).
Could be couple of probs.
1) faulty expansion vessel
2) faulty pressure relief valve
3) system getting too hot

Give the red valve a twist til it clicks, this will open and close the valve and may fix the leak, if not get a competent plumber who is qualified to work on unvented systems.
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