Need new boiler, British Gas quote, need some advice/ handholding

[whataboutbob]

My Dad died in January and used rent out a house to a family, at a low rent. It is currently in probate. It turns out the tenants have been soldiering on with an old boiler which now needs replacing (Dad had the Landlord's contract with BG so they were providing free repairs/ services etc). BG now say it needs replacing, but also that it can't be put back in the same place as the flue is "illegal", the pipes will need to be re routed and the flue taken out via the roof. They have quoted £4900 for the work. I obviously need to deal with it and pay for the work, but just wondering about not going with BG.
My record for finding good independent traders though has been woeful, my last plumber disappeared mid job, and previously I employed a builder to do a flat renovation and unbeknown to me he botched the new shower leading to burst pipes and irate downstairs neighbours (both were personal recommendation/ found on Which ? trusted traders). So should I try and find an independent again for quotes, or just bite the bullet and get BG in with their big prices? I'm in the SE. Thanks for any advice/ insights.

Thanks sunny it's really useful to get an idea of the sort of prices people are getting quoted. Thanks also for the recommendation buffalo.
Piglet I have googled Checkatrade complaints, quite sobering.

2nd company has got back to me saying they want to put the new boiler in the loft. I'm not too sure about that. There's no retractable ladder to get up there so the tenants would have to improvise something to get up there if they need to check on the boiler. Probably not the best idea- what does everyone think?

many menders won't go up to repair boilers in lofts unless there is a fixed ladder, a safety-rail round the hatch, fixed flooring and lighting.

I am concerned that it is an unheated part of the house so more at risk of freezing, and any odd noises or smells will not be noticed as quickly as if it was in, say, the kitchen. Modern boilers can be very small and quiet.

I wonder what made them suggest the loft.

BG wanted over £8000 recently to do my parents CH & combi boiler from scratch house had no heating in at all This was for 8 radiators and a large towel rail ( not including gas connection which was £700
This is a big standard 2 bed terrace house .

In the end they paid £4500 With a independent local company

Well, I got 2 other quotes and have decided to go with the 2nd local firm. I liked the lady who runs the company, she seemed very straight (God I hope I don't get to eat my words). They basically quoted all or most of the points/ works BG listed, but for £1000 less. The main difference is they will use a Vaillant boiler not a Bosch, but it has a 7 year guarantee. They guarantee labour 1 year.
I 'll still use BG's Homecare plan and their gas safety checks, but if the independent does a good job I will use them again.
Thanks to everyone who encouraged me to wean myself off my BG reliance!