House odour

We had a odd smell in our bedroom....turned out to be a bee nest in the corner of the roof....could not be removed as they are protected but once all gone, hoovered and nest removed the smell disappeared!

You don't have an en-suite in the spare bedroom?
Waste water pipes that don't get used will start to stink after a few months, but a quick squirt of bleach and some running water clears it.

We had a strange smell in a spare bedroom. Then we could smell it elsewhere, even in the garden. To cut a very long story short it turned out to be coming from next door where there was a cannabis factory! This was quite a few years ago and I still can't believe that we never suspected a thing until we noticed the smell.

When I read through the OP, my first thought was 'dead mouse', then found that subsequent posters all had the same thought. Luckily we haven't, fingers crossed, ever had one in the house. But, during a coach trip in China, we suffered from the smell, At first we blamed the driver, his lunch, anything that we all could think of, and the driver was not amused, it was a new coach and his pride and joy. It turned out to be a dead mouse in one of the ventilation/heating pipes. After a good clean, the pong was gone.

I think it is more than likely a dead rodent. We had one under the floor of our last house and in the first instance, like you, sent for the gas people because we thought it was a gas leak. Eventually, DH went down into the crawl space under the floor and found a dead rat. No idea how it got there, but we never had trouble after it was removed.

Years ago, teenaged DS1'S bedroom had an awful smell. I spent ages looking for stray socks festering aomewhere but the smell just got worse and worse. We eventually found a bird which had presumably fallen down the chimney and died in the boarded up fireplace. Yuck!

I used to help run a community centre and when I unlocked in the morning I would get a strong whiff of a horrible smell. Turned my stomach. This went on for a week or so, no one else smelt it as by the time they arrived fresh air had gone through. One day it was so bad I ended up crawling around the seating area where I thought it was, sure enough found one spot where it was terrible. Built in seating, got someone to pull the top off and inside were two dead rats and the smell nearly knocked you off your feet We called in pest people and it turned out that the local council had put poison down some drains a couple hundred yards away and the rats had eaten that and then followed pipes under the building and got up under the seats through old pipe, and there they died. It had to sprayed with some special (very fragrant) stuff which cleared the stench.

Or even a rat Marelli the smell is like a putrid gas. It’s a pity DH cannot smell it he doesn’t have a sense of smell and isn’t too bothered.

There was a really horrible smell that suddenly appeared in our spare room, Elizabeth 1. It was last summer, and we searched under the bed, thinking perhaps the cat had brought in a mouse or bird - which she had. A bloated and purifying mouse was lying just under the edge of the bed's valance. The smell was awful and goodness knows how long it'd been there. I know you don't have a cat, but a wee mouse might just've come in out of the November weather?

Apparently a dead mouse gives off a gassy odour. Could that be possible? They can squeeze into anything larger than the width of a pen.