Dripping bathroom taps - simple fix or larger problem?

[as24]

Hi to all,
Seeking your advice here - a very long back story to get you well informed:

We have a small two-storey home, with a bathroom on each level.
The house is about 80 years old while the bathrooms were both rebuilt and fully renovated 10 years ago (downstairs bathroom renovated, upstairs bathroom built from scratch)
The shower in both bathrooms has been used daily during these past 10 years.

About 2 years ago, the shower head in our ground floor bathroom would heavily drip for about 30 seconds, beginning roughly 1-2 minutes after the shower had been used and turned off.
For the first 8 years, the shower head did not drip after a shower.

I didn't think much of it at the time, other than needing to put a bucket under the shower head to catch the excess drips.
~6 months on and the drips from the shower head decreased a little after each shower, however I noticed the shower's mixer tap began having a small drip that would occur about 3-5 mins after each shower, then stop after a few minutes.

A few weeks later the shower's mixer tap would be dripping sporadically throughout the day, often occurring when, or just after, other areas of the house had been using water, such as the ground floor's bathroom sink or toilet, as well as the upstairs shower and sink taps.
Our ground floor bathroom also has a standalone bath (which is very rarely used), yet in the last few months, the mixer tap for the bath has also developed a drip – albeit very minimal; approx 2-3 drips per day into a small container catching the excess drips.

A few months back, we stopped using the ground floor shower (only showering in the upstairs bathroom), to see if that would have any impact on the dripping mixer tap - it did not.

What may or may not be relevant, over the last few months since we have all been using the upstairs shower, that shower has now also started to have a brief drip from the shower head at the conclusion of each shower. Thankfully this upstairs shower head only drips briefly after a shower and not throughout the day.
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Last week I went about replacing the cartridge in the downstairs shower.
I turned off the mains water supply and then went back into the bathroom to turn on the shower to get the last of the water out of the system.
Turning on the shower, the water first came out as a normal stream lasting about 1 second before easing into a steady drip as it should have.
30+ seconds later, the shower tap was still dripping which was odd.
I went over to the bathroom sink and turned the tap on - no water came out of there as expected.
I then went to the upstairs bathroom and heard water passing into or through the cistern of the toilet.

That was a surprising find as it had now been about 3-4 minutes since I had shut off the mains water.
The toilet had not been flushed during this time, so I have no idea why (or how) there would be water passing into the cistern.
I had a quick look into the toilet bowl, but didn't notice any overflow water running into the bowl from the cistern.

I turned off the toilet's shut off valve, the water sound in the cistern stopped and when I went back to the downstairs bathroom, the slight, but continuous, dripping from the shower tap had stopped as well.

After replacing the shower's mixer tap cartridge, I turned on the mains water supply and then went back to the upstairs toilet and turned the shut off valve back on (open).

Since replacing the cartridge 5 days ago, the shower's mixer tap has not dripped at all.
However, we have not yet used the downstairs shower in this time, as we have remained showering in the upstairs bathroom.
What has happened though is that the mixer tap of the bath (in the downstairs bathroom) now drips alot more, after someone has had a shower in the upstairs bathroom (2-3 drips per day now upto 100-200 drips per shower).
When the upstairs shower is not in use, the bath's tap still produces it's normal 2-3 drips per day.

As a test, I turned off the shut off valve on the upstairs toilet prior to my last shower.
I had the shower, then went and checked the container under the bath's mixer tap and found that there had seemingly been no drips during the shower. I went back and turned on the upstairs toilet's valve and came back to the bathroom to find the bath tap slowly dripping (presumably the build up from the shower). The dripping stopped after a few minutes.
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My questions;
1) Why is the upstairs toilet's shut off valve having such an impact on the drips in the downstairs bathroom?

2) Should I simply replace the bath's mixer tap cartridge and see if that fixes the problem, or is it clear that our property may have a more complex problem such as water pressure issues that requires a plumbers attention rather than a DIY job?

Thank you.

[MitchellMc]

Welcome to the Bunnings Workshop community @as24. It's fantastic that you've joined us, and many thanks for the questions regarding your leaky tap and fixtures.

It's great that you have provided the backstory, as it should assist our members in offering their opinions. 

In my opinion, your testing is likely revealing some issues and also giving you false positives. Just so you are aware, it's normal for showerheads to drip after a shower as residual water left in the head needs to escape. The discrepancy between how long it drips for since new and now, could have to do with calcium and scum build up in the head. My showerhead drips for approximately a minute after a shower, and if I tap the head and shake the water out, it will stop.

Any fixture that drips well after its usage or just randomly needs its washer or ceramic cartridge changed. Fluctuations of the pressure in the lines whilst using other fixtures are likely causing the dripping, but that doesn't override the fact that they wouldn't drip if the valve washer or ceramic cartridge weren't worn out.

One of the false positives I can see is that you gave the shower enough time to stop dripping whilst you turned the toilet inlet valve off. I'd suggest it is just a coincidence that the dripping stopped afterwards, and it's more likely that there was no more water left in the head.

It's all a bit of a mystery at the moment, and likely some of the issues are interconnected and some co-incidences. I'd suggest you start narrowing down the issues by replacing the valves or cartridges in the taps that leak spontaneously or when other fixtures are being used. As you've experienced with the shower, when you replace cartridges, the leaking stops. 

I believe you are experiencing some unusual effects with aged valves and cartridges, and I'm fairly confident replacing them will solve the issue. It's unlikely there is anything more sinister than that going on.

Let me mention @redracer01 to get his opinion.

Please let me know if you have any questions.

Mitchell

[redracer01]

Hello @as24 

This use to happen to my rental property before the hot water cylinder failed. If the renovation occurred  10 years ago, it is prudent to check your hot water cylinder to see if any of your HWC ( hot water cylinder ) valves have malfunctioned or showing signs of wear and tear. The most common culprit is the hot water expansion valve and the cold water expansion valve. You say nothing happened in the first eight years and then all of a sudden it starts to leak? Yet the seals and cartridges look sound? Odds are that there has been a valve failure or the other cause is incremental pressure from the council has been making its way in to your plumbing system. Again a possible valve failure the water pressure regulator. The drip from bath spout could possibly be the weakest point in your plumbing set up in the house. Hence the excess pressure from the water finds its way to weakest point and comes out there ( change cartridge or jumper valves to secure the seal ). Your toilet possibly could be carrying the largest amount of water pressure in its pipes as even after turning the water off the excess pressure in your system manages to push the water out and in to your cistern despite the water being turned off. In this instance I would recommend getting a plumber and have him do a water pressure test. By doing this test he can diagnose if there has been a valve failure. He can then proceed to replace the HWC valves that have failed. Most of the valves and even the hot water cylinder are rated for an average run of 10 years but even before that parts fail.  It would not hurt to renew the jumper valves and cartridges of your current taps in the house to give you another 8 years of trouble free showers! It may seem like our HWC's are indestructible but like all items in our house we must keep an eye on it even it seems like there's nothing wrong with it. I hope my suggestions help.

Cheers,

Red

[as24]

@MitchellMc @redracer01 - Thank you both very much for your detailed replies and information provided.
It supports some of my theories as I was leaning towards getting a plumber in the check the water pressure first, as my concern was replacing the cartridge of the bath's mixer tap would only move the leak onto a different fixture in the house (perhaps one in a more hidden/less seen location eg. outdoor taps or laundry room).
I appreciate your help and advice.

Cheers