15mm pipe to 22mm shower going cold

30 Nov 2004
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United Kingdom
I am trying to troubleshoot a problem with my shower losing pressure, pressure drops boiler cuts out pressure returns and boiler kicks in again etc. etc. step back wait long enough it will get warm again but not for long.

I have tried a couple of times to get some advice on this forum but no one has got back so I have been scrabbling around in the loft tracing pipes and hope the extra info will generate a reply.

I had a new worcester bosch 30i boiler fitted to replace old gravity back boiler. The hot feed from the boiler was 15mm feed then joins to 22mm with elbow joint I am assuming the plumber that fitted the new boiler used the old 22mm pipe and somewhere farther on it is changed back to 15mm.

When the bathroom fitter a month later fitted the shower he joined the 15mm pipe for the shower to where the pipe sizes changed and replaced the elbow join with a T join. So what I am needing advice on is, is the 15mm pipe feed to the shower in competition with larger 22mm pipe and the reason I am losing pressure to the shower.

The shower is a mira digital with mixer in loft and the mixer box is situated slighter higher than the 22mm feed, so the 15mm feed to the box has a slight gradient. Had a guy from Mira 10 days ago if he did spot it he didn't mention it, just stuck in a new mixer valve. The shower had been banging and vibrating it fixed that, no problem. The noise had been so bad didn't notice if the pressure loss was a problem then, hadn't been able to stay long enough to find out!

Grateful for any feed back.
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