Should/would a builder guarantee work on a leaky roof for 6-12 months?

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Feeling at a bit of a loss about how to deal with this and would appreciate some advice.

We have damp/ a leak in our bedroom - damp patch over the window and a line of damp which obviously follows the beam above and is leaking brown-stained water (presumably from the wood beam).

There's a dormer window in the room above and this is probably the source of the water we think.
The thing is, we had work done on the dormer about 7 years ago which was expensive and meant to fix a similar problem. We've had smaller leaks in different places over the years, which makes me think it didn't completely solve it.

It seems that roofers will come out and say 'we can do this, this, and this and it'll be £1500' but none are able, or willing, to guarantee that it will fix the problem.

Is this normal, or should I be pushing for some sort of guarantee that they'll come back if the problem returns?

Hi - we had a similar problem too with leaking in my mum's living room on and off over the years, it got horrendous recently with leaks in about 5 places incl around the light fitting! Several roofers came, did patch up jobs but no proper guarantees though to be fair one did return for free after it started leaking soon after he'd worked on it. Most said they could only guarantee a new roof. Just a few weeks ago we had further work by a firm that did more expensive repairs, cost nearly £4k but touch wood it hasn't leaked since and it's been really tested with recent heavy downpours. They have given us a 10yr guarantee but until it leaks again am unsure if they will honour it. Most roofers who visited wanted to do full or partial roof replacements, it's a v old house and isn't in a great state but spending £15K+ isn't an option. If you're London based, send me a PM and I'm happy to give you the name of the roofer we used although they are quite booked up. It's incredibly stressful to have a leaking roof and I came to dread the rain!

I've only heard of guarantees for completely new roofs, but others may know different.

In my experience roofers are a law unto themselves. You're lucky if you can find one to quote and do the work in the first place. You could try to persuade them to come back if it's immediately apparent that the repair has failed, but I doubt they would come back after any period of time has elapsed - they would just say it's a new problem. Try to get lots of quotes, and go with a recommendation from someone you know if you can. I had someone come out who I found on Check-a-Trade, who quoted me for works totalling £6K (which he wanted in cash). It turned out that almost all of the works weren't necessary.

The problem is that because water will ingress and run along in strange ways roofers can fix problems they can see but they can't guarantee that any visible roof defect is what is cause water to come in.

It's very hard to work out where a leak is actually coming from.

Rooves are quite complicated.

So nobody is going to be prepared to come out and promise a fix unless they redo the whole roof in which case they can be confident.