Blockage or airlock in hot feed to mixer shower


Postby johnch » Wed Dec 16, 2009 1:39 pm

I've recently replaced an old mixer shower with a new one - using the existing hot and cold feeds without making any changes to the pipework at all (except for new adaptors at the top to fit the new mixer). When I turn all the water back on the shower only runs cold. I've removed it to check the incoming water (ie to see if it's the shower itself that is the problem - and I don't think it is) - the cold runs fine, but there is no flow at all out of the hot pipe (and I have double checked to make sure I haven't left a valve closed !) Is there an easy way to clear this blockage or airlock in the hot supply to the shower ? (both the hot and cold are gravity fed and I don't have a pump fitted)
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Postby rosebery » Wed Dec 16, 2009 10:41 pm

Did the old one work?

Have you replaced a manual mixer with a thermostatic one?

Do you mean that there is no flow out of the hot at all with the mixer disonnected or with it connected?

Is the shower piped so that both the hot and cold supplies are independent from other services? The shower needs iit's own supply and should not be competing with other draw off points like taps. That is cold out of dedicated connection in CWST and hot via an appropriate flange.

ANother possibility is that there is insufficient head between the cistern level and the outlet from the cylinder. What is this height in metres?

How close is the feed to the shower from the outlet at the top of the cylinder? What are the pipe sizes involved?

Sorry lots of questions with few answers at present.

Cheers
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Postby johnch » Mon Feb 08, 2010 9:12 am

Hi rosebery - thanks for your reply - sorry for not answering your Q's earlier - I broke my PC, so have been out of email contact for ages ... !

Here are the answers to your questions:

1. The old one did work - although the temp control was variable, and the only way I could get a warm shower was to partially close the isolation valve on the cold feed (even with a tankl full of hot water).
2. I'm not sure whether the old one was a mixer or thermostatic - could have been either, probably the cheapest type available when the house was built.
3. I think both have independent supplies - ie as I isolates both feeds when installing / tiling etc and used everything else in the house OK.
4. "insufficient head between the cistern level and the outlet from the cylinder. What is this height in metres?" Do you mean the height between the outlet from the cold water tank and the outlet from the hot water cylinder? (Sorry for not understanding exactly). If so, this is probably about 2 - 2.5 m.
5. According to the instruction manual I have enough head space - I estimate the distance between shower head and cistern outlet to be between 1.5 and 2 m. The manual specifies 1m minimum. The pipe sizes are both 15mm.

Cheers, John
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Postby johnch » Mon Feb 08, 2010 11:12 am

Sorry - missed one of you questions:

"Do you mean that there is no flow out of the hot at all with the mixer disonnected or with it connected?"

There is no flow out of the hot at all - either with the mixer connected or disconnected. When I first installed the mixer and it didn't work, I removed it (After isolating both hot and cold feeds) and checked both to see if I had a flow. COld was OK, hot didn't appear to have any flow at all. However, as I stodd there scratching my head, hot water started dripping and then gushed out. I isolated the hot feed again (mopped up!) and reconnected the mixer. No hot shower possible ... so I isolated both feeds, removed the mixer, and now, when the hot feed is turned back on no hot water comes out at all - even after standing there scratching my head ... Seems very strange I know (no doubt it'd start to work if I left it and went to the puib for a couple of hours, but that could be a little damp ...). That's why I think I have some sort of blockage / airlock in the system ...

Cheers, John
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