In the last 2 weeks I've noticed a horrible smell coming through the floorboards of our home, the smell seems concentrated in the kitchen.
We initially thought it could be a blocked toilet pipe, although the toilet itself isn't backed up, so called out a drains company.
They couldn't find any obvious issues after checking manholes, drains etc.

Our house is raised approx 2 feet from the ground and he did lift a floorboard and the smell is definitely coming from under the house. After taking pictures, and without raising the whole floor at cost, he couldn't see any obvious issues. It was dry and debris free apart from usual builders rubble.
This led him to think that perhaps a rodent has died under our house and this was the smell.
I'm not convinced by this and wonder whether the boiler could be a potential cause. The water pressure is low under 1 bar and the boiler itself is a bit erratic - could this indicate a leak? Could the leak have led to damp floorboards that are not visible?

I think the dead animal is the most likely issue... YOu probibly do have boiler issues... but I doubt they could cause the smells you describe.

Thanks, I appreciate your answer. It's difficult to tie down what the smell... smells like... if you see what I mean. I'm not sure I would know the difference between moldy timber / decomposing animal.

Dead animal tends to have a sweet component to it.. it's different than rotting fish.

Have you ever had a piece of raw meat in your refrigerator you planned to cook the next day but it ended up being a couple days... you smelled it... but it smelled a little strange, unlike a fresh piece? Magnify that strange part of the smell a lot. Its one of those smells that once you get a nosefull of it you don't soon forget it. One of those things just thinking about it you can actually smell it again from memory.

This is it, the smell in our house is more musty I think. Without an obvious problem it's difficult to tie it down.

Yeah... musty is a very different odor. Musty indicates you really need more ventilation in the crawlspace, and might have mold issues as a result.