Smoke alarm works with test button but doesn’t detect smoke!

[Fivemorenights]

Kitchen just filled up with smoke and the downstairs alarm didn’t go off. I test it religiously every week and it works fine.

I’ve just held a smoking bit of paper under all three of them and none of them went off, but work fine when the test button is pressed.

They are wired in, landlord provided them. Urgh I’m not going to be able to sleep tonight!

Is it definitely a smoke sensor alarm or is it a heat sensor one?

Different types: www.fireservice.co.uk/safety/smoke-alarms/

Check it's not a heat sensor. Sometimes near a kitchen it's heat sensor as smoke ones go off every time you burn your toast or cook bacon. Can you test by blowing hair dryer at it?
Maybe check with landlord though.

Ok I had no idea there were heat sensor ones!!

Will check with hair dryer

We have an optical one nearest the kitchen, they are less likely to go off with smoke, say from burning toast.

No it still didn’t work! I’m going to go out today and buy some battery ones. I can’t believe we’ve not had working smoke alarms for two years, I feel sick!

Do you vacuum them weekly? I ask because a build up of dust can cause the sensor not to work

Heat sensors are likely to be set far higher than a standard hair dryer could trigger, so I'd try steam from a kettle before buying new ones.

Heat detectors measure the change in temperature over a period of time and activates at a certain temperature. You won’t get them to go off with a hair dryer.

www.aico.co.uk/product/ei144rc-heat-alarm/

Don’t try steam from a kettle, that won’t do the detector any good at all.

If they work at the test switch then they work.

Surely the test button just tests the alarm and battery are functioning, not the detector itself?

Sorry if the kettle is a rubbish suggestion - my ex had one in his kitchen that went off if you opened the oven door too quickly, so I didn't think they could be so easily damaged.

The test button tests the alarm is functioning. People don’t usually test their smoke alarms by lighting fires so why would you need to test a heat detector by physically testing it, they’ve got a ten year lifespan. They go off at 58° ( and when I did my training I’m sure they said that they measure the rise in temperature over a certain time) . You shouldn’t be going off under normal household conditions, that’s kind of the point in them.

I unscrewed it, it’s a smoke alarm not a heat sensor.

I held a smoking bit of paper underneath it and it’s covered in black soot now and still didn’t go off. They aren’t working

Smoke alarms do have a limited life span (about 10 years I think), separate to the power supply/battery life. The sensors degrade eventually.
If you can, I’d pick up some cheap ones to tide you over Christmas and let the landlord know the mains ones need to be replaced.