Shower hot water pressure loss

[Peter Johnson]

I have a Mira 88 shower which draws hot water from the main hw tank. It has worked satisfactorily for several years until this morning, when the only way I could get hot water out of it was by removing the shower head and lowering it, which is ok for washing my feet but no good for anything else. Doing this I can get a good flow of hot water but it stops as soon as I put the shower head back on its bracket. I have checked the hose and the shower head and they seem to be ok. It seems to me that there is a reduction in pressure on the hot water but I can't work out why. Any ideas? (The hw tank is on the first floor, the same as the shower, so the rise is just a few feet into the roof space.) TIA

[John]

Is the cold water tank filling properly? Is there any foreign body in the outlet in the bottom of the cold water (Header) tank?

[BigWallop]

This system is cold water storage tank fed? The cold water tank is in the loft? The hot water cylinder is one floor below the cold water tank? The shower room is on the same floor as the hot water cylinder?

If the answers to these questions is yes, then make sure your cold water tank is filling properly, because the actual pressure for this system is coming from the highest point in the cold water storage tank.

If you answered no to any of the questions, then can you explain what is different?

[Peter Johnson]

Your analysis is correct. I will investigate the tank in the loft tomorrow. Thanks.

[robgraham]

I had to resolve a not dissimilar problem in my daughter's house some years ago. I never did see what was causing a blockage in the cold water feed to the hot tank, but I had to back flush the system with a hose between the the mains tap and the hot tap, having drained down the cold tank first. That didn't work initially but loosened up whatever it was for the problem to disappear an hour after I'd given up!!

The suggestion was that the blockage was caused by a slime film build up.

Rob

[Olav M.]

[Peter Johnson]

I've been in the loft and the tank was full, lid in place. I turned the water off and drained the hw, all ok and nothing obviously blocking the outlets. Tank refilled ok but no improvement in pressure. It's now obvious, as well, that hw pressure is low at the taps but obviously it's more noticeable when the shower doesn't work. I think I'm at the limit of my capability now. I've got a plumber coming tomorrow. Thanks to all for comments etc. I'll report back.

[Peter Johnson]

Plumber arrived 10 minutes early, looked at the installation, explained that he would try the tank blow-back method and asked me to turn off the water preparatory to draining the header tank. Whilst I was doing that he took the head off the shower, held the hose downwards and turned the water on - result air lock blown out, everything now ok. No charge for that so he's coming back to flush the central heating, which I was recommended to do two years ago.