Changed battery to one smoke alarm and now other goes off continually

[Guest Susan Longley]

We have 2 smoke detectors, one upstairs and one downstairs, both on landings. They are Ei141 mains with battery. The downstairs one was beeping and driving us insane so we presumed the battery needed changing. The smoke alarms are 5 years of age as were fitted into new build property by the builders and house is nearly 5 years old. With great difficulty and after watching your video, we changed the battery in the down stairs smoke alarm after turning off the mains. We had an extremely difficult time trying to remove the bottom part of the alarm, which housed the battery and I could not remove it and my husband is a bit heavy handed, but managed eventually to remove with force. Refitted smoke alarm downstairs - again not easily. On turning on the mains to the smoke alarms, the alarm upstairs goes off as if there is a fire and does not stop until the mains is turned off. Obviously this is not ideal. I have tried cleaning both alarms, with hoover to remove any dust particles and also wiped outside of units and dried off as info on your website. I have also changed a bulb in the downstairs landing in case there was any problem with wiring, but this has made no difference. Every time the mains is turned back on, the upstairs smoke alarm goes off loudly.

Any advice would be appreciated as I think my next step will have to be an electrician. Would it be worth getting a replacement base in case this has been damaged by my husband, although when mains is turned on, both smoke alarms show green light?

[Safelincs]

I think Shawn to this one :-)