Sludge in hot water pipe

3 Nov 2006
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United Kingdom
The flow out of the hot tap in my daughter's kitchen reduced over the past couple of weeks to little more than a trickle.

A combi boiler supplies the house and mains water pressure is at the low end of the boiler's acceptable pressure limits. There are two other hot taps in the bath room above the kitchen and the boiler is in a bedroom cupboard slightly higher than the bathroom taps.

The property is ten years old and this is the first ( known ) occurance, certainly not in the five years my daughter has lived there.

Suspecting an air lock in the pipe the kitchen hot tap was back feed with cold water from the mains pressure cold tap while the hot taps in the bath room were both fully open. At first water out of the bath tap was clear, then dis-coloured and then a considerable amount of black and brown material came out followed fairly soon by clear water.

Do combi boilers create solids in the hot water and would this then settle and accumulate in the lowest part of the hot water system ? Or could there be another problem.
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Sounds like you have a problem with your Plate Heat Exchanger, if your mystery boiler has one
It is from memory a Potterton ( head office in Preston ) something 80.

I was fearing a boiler problem. If there is a leak across the heat exchanger would the pressure in the radiator system eventually increase to the same pressure as the incoming mains supply and would that be a clear indication that a new heat exchanger was needed ?
Combi 80 has no plate heat exchanger.

The incoming cold supply to this boiler does have a filter and flow regulator.

I suspect this is your problem
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If the plate heat exchanger was blocked it would affect all your hot taps fed from the boiler, not just 1? As said though, there's no plate heat exchanger.

A blocked filter/flow regulator would also affect all hot taps though ......?
I was "diagnosing" and guiding by phone.

The filter in the boiler inlet being blocked can not be the problem as hot flow to bath room is good. It was only the kitchen sink hot tap where flow had reduced over a period of a few weeks.

My thought is lime scale or other deposit being formed in the bolier and washed out into the lowest part of the pipe work but why brown ?
use a magnet to detect any sludge in copper pipework, it it sticks there is sludge inside.
use a magnet to detect any sludge in copper pipework, it it sticks there is sludge inside.
That's assuming the sludge is ferrous, like you'd find in a heating system, not bits of a tap washer, limescale, solder, PTFE tape, plaster, sand, mud, cement, polyfiller, paint, etc, etc. which could have found it's way into the pipe, possibly even before it was installed, and eventually found it's way towards the kitchen tap.

Is the kitchen tap connected by a flexi connector? Could it be kinked? Or past it's sell by date?

I once had a tap washer stick to it's seat and tear the fixing screw out through the hole in the middle, so it just let a dribble of water out through the screw hole.

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