Pipes old and new joined together
We moved into an 1970-1980 Bungalow and it would appear the water feed originally came from an attic tank, the feed was then changed to mains supply and each house has it's own water drain covers in their drives.
We have water hammer issues in the bathroom and the pipes to the sink look odd, in that the old metail supply pipes are still in situ but a new pvc pipe comes from the floor some inches away and is connected to the old pipe by a T piece wheich then has tails to the taps.
Why has the pvc pipe been t pieced to the top of the old pipe rather than directly to the taps and can this set up be the cause of the violent water hammer when turning taps off?
Perhaps air in the old pipes?
I would have thought they would just be bypassed and not teed together... any advice anyone?
I have pictures of the set up but unsure how to post them here...
Advice from 4 local tradespeople
Yes — that odd tee arrangement could absolutely contribute to water hammer, and your instinct is sound: on a mains conversion, I would normally expect the old tank-fed pipework to be properly disconnected or fully repiped, not left as a strange branch unless there was a reason to reuse part of the existing tap tails or fittings.
A few points:
The most likely reason the newer plastic pipe has been teed into the old metal pipe is simply convenience. Someone probably wanted to pick up the old final connections to the taps without fully reworking the basin pipework. That is common enough on older bungalows, but it is not always the neatest or best hydraulic layout.
What concerns me more is this part:
The old metal pipe is still present
A new plastic pipe joining it with a tee
violent hammer when taps shut off
That can create a dead leg, an odd branch, or / poorly supported mixed-material run, and any of those can worsen banging. A rapid stop causes water hammer or a change in water flow, and pressure surges can be made worse by fast-closing valves, trapped air, or poor support. Water Regs UK notes that rapid valve closure can cause transient surges and that pressure-reducing valves or surge arrestors are sometimes used to control them. Wavin's technical guidance also notes that trapped air and rapid flow changes can cause sharp pressure rises.
So, to your specific questions:
Why tee into the top of the old pipe rather than go directly to the taps?
Most likely because it was quicker and cheaper, or because the installer wanted to reuse the existing final metal tails/tap positions.
Can that setup cause violent water hammer?
Yes, it can contribute. Not necessarily because the old metal pipe contains "air" forever, but because:
The branch arrangement may create an awkward pressure wave
The old pipework may be loose or poorly clipped
The taps may be shutting off the flow quickly
The mains pressure may now be much higher than the old tank-fed layout was designed for
Is air in the old pipes the main issue?
Usually not as the only cause. Air can aggravate the hammer, but in a long-standing system, the bigger suspects are:
high incoming mains pressure
quick-closing tap cartridges
loose or unsupported pipework
a dead leg / redundant branch
a failing fill valve, stop tap, or pressure issue elsewhere
My view: the tee arrangement is not ideal, and in an older bungalow converted from attic-tank supply to mains, it would be sensible to have that section reviewed. A neater direct run to the taps, with proper clipping and possibly a pressure-reducing valve or hammer arrestor if pressure is high, is usually the better long-term answer.
What I would check next:
whether the banging happens on hot, cold, or both
whether it is worse when the basin taps shut quickly
whether the pipework under the basin is loose
whether your incoming mains pressure is high
whether there are any redundant capped branches/dead legs on the old layout
A good practical test is this:
Turn a bathroom tap on moderately, then shut it slowly. Then repeat and shut it quickly. If the hammer is much worse on quick closure, that points strongly to pressure, valve closure, and pipe support/layout rather than a trapped-air issue.
So, in plain terms:
No, I would not say that teeing the new plastic into the old metal is best practice if it leaves a strange branch arrangement. Yes, it could be part of the hammer problem. And yes, I would be looking at repiping that section more cleanly rather than just accepting it.
If you upload the photos, I'll tell you exactly what looks wrong.
Regarding water hammer that can be from taps with rubber washers, ceramic disc cartridges.
Toilet or header tanks in the loft space.
the traditional type ball valves (arm with a float at the end) or torbec inlet valves also.
High main water pressure and pipework not clipped can also add to the problem.
An engineer visit would be required to investigate and locate the cause accurately.
The T-piece is likely used to avoid disturbing the existing pipe run to the taps. Tapping directly into the pipe could weaken it or require significant excavation, whereas using a T-piece allows for a new branch to be added without needing to cut or significantly alter the original pipe. Additionally, a T-piece can help manage water flow and pressure, especially when connecting to a new tap.
Whoever did the job took a shortcut. They T’d into the old pipe instead of running a proper new line. That old pipe’s probably causing air traps or pressure issues which is why you’re getting water hammer. Best fix Cut out the old bit and run new pipe straight to the tap.
