LNER Azuma Controlled Emission Toilets

ryan125hst · 24 Jun 2026

When boarding an Azuma (800206) to travel from Doncaster to Retford after attending the event at Wabtec Doncaster on Saturday, the smell from the CET tanks was noticeable while standing on the platform at the toilet end of coach C. The smell was also present inside the carriage, not quite as strong but noticeable. This was on the 14:52 to London Kings Cross (ex York) and so wasn't a service right at the end of the day when the tanks are more likely to be full.

It was the first time I had noticed this although admittedly I've not travelled on Azumas that many times. I know everyone used to (and perhaps still do) moan about the toilet smells from the Voyagers. I wasn't aware there were issues with the Azumas with this. Was it the warm weather causing the smell, a tank that hadn't been emptied, or is the CET smell something that is plaguing the type?

RailUK Forums

AdamWW · 24 Jun 2026

ryan125hst said:
When boarding an Azuma (800206) to travel from Doncaster to Retford after attending the event at Wabtec Doncaster on Saturday, the smell from the CET tanks was noticeable while standing on the platform at the toilet end of coach C. The smell was also present inside the carriage, not quite as strong but noticeable. This was on the 14:52 to London Kings Cross (ex York) and so wasn't a service right at the end of the day when the tanks are more likely to be full.

It was the first time I had noticed this although admittedly I've not travelled on Azumas that many times. I know everyone used to (and perhaps still do) moan about the toilet smells from the Voyagers. I wasn't aware there were issues with the Azumas with this. Was it the warm weather causing the smell, a tank that hadn't been emptied, or is the CET smell something that is plaguing the type?

Not been on many "Azumas" but I've done plenty of trips on the GWR IETs and have never been aware of this.

tfw756rider · 25 Jun 2026

ryan125hst said:
Was it the warm weather causing the smell

Probably, yes.

When the CET tanks get hot on any train with them (which nowadays is pretty much all trains with toilets, so most trains on the British network),

they 'vent' (with a leak-proof 'gooseneck' vent), otherwise the increased pressure buildup from the gases (caused by the heat) could potentially rupture the tank.

When the tanks are 'venting', the train becomes smelly on the outside (like you experienced outside your 800/Azuma), but it's either that or the tank potentially ruptures.

Oh, and by the way, the tanks can also start 'venting' at any time (such as when I was part-way through drinking a milkshake by a 197), which was a nice (!) surprise...

81A · 25 Jun 2026

Also never noticed despite regular journeys on class 80x (mostly GW though).

ryan125hst · 26 Jun 2026

tfw756rider said:
Probably, yes.

When the CET tanks get hot on any train with them (which nowadays is pretty much all trains with toilets, so most trains on the British network),

they 'vent' (with a leak-proof 'gooseneck' vent), otherwise the increased pressure buildup from the gases (caused by the heat) could potentially rupture the tank.

When the tanks are 'venting', the train becomes smelly on the outside (like you experienced outside your 800/Azuma), but it's either that or the tank potentially ruptures.

Oh, and by the way, the tanks can also start 'venting' at any time (such as when I was part-way through drinking a milkshake by a 197), which was a nice (!) surprise...

That makes sense. How long would a tank normally be venting for? It was still noticable when we got to Retford.

On a related note, I noticed there was a set of green LED's and another set of amber LED's under train as I got got on, I believe where the CET tank is (I was looking as I wondered if the tank was full).

Are these the CET and water level indicators as I know some trains have them?

tfw756rider · 26 Jun 2026

ryan125hst said:
That makes sense. How long would a tank normally be venting for? It was still noticable when we got to Retford.

Getting a bit beyond me, but I suppose for as long as it's hot enough for the vent valve to be triggered open.

As for the smell getting inside, it might have something to do with it reaching the 800's air conditioning intake vents (but again, I'm not entirely sure, but would make sense. On 158s when the 'emergency windows' are open and the tanks are venting, the smell definitely goes inside through those windows, indicating that it goes up to that top-side area of a train in general).

ryan125hst said:
On a related note, I noticed there was a set of green LED's and another set of amber LED's under train as I got got on, I believe where the CET tank is (I was looking as I wondered if the tank was full).

Are these the CET and water level indicators as I know some trains have them?

Most likely, yes. I'm not familiar with the 800 ones, but on the retrofit tanks for the ex-British Rail trains, there tends to be an amber LED/light and then a red one depending on how full the tank is, to warn that it needs emptying.

This is a lovely discussion :lol:

ryan125hst · 6 Jul 2026

tfw756rider said:
As for the smell getting inside, it might have something to do with it reaching the 800's air conditioning intake vents (but again, I'm not entirely sure, but would make sense. On 158s when the 'emergency windows' are open and the tanks are venting, the smell definitely goes inside through those windows, indicating that it goes up to that top-side area of a train in general).

Hopefully they've been designed in a way to reduce this after the issue with the Voyagers!

azOOOOOma · 6 Jul 2026

I’ve definitely noticed that there’s a noticeable whiff over the last week since the weather has been hot and humid. Not nice!

LNER Azuma Controlled Emission Toilets

ryan125hst

Established Member

RailUK Forums

AdamWW

Established Member

tfw756rider

On Moderation

81A

Member

ryan125hst

Established Member

tfw756rider

On Moderation

ryan125hst

Established Member

azOOOOOma

Member