Hi Simon, Yes happy to help and I’m sure other experienced landlords will want to give their views, too 
Regarding the example of the carpet, this is a great case to illustrate how deposit deductions work.
In general, you can ask to deduct any costs for damage if you feel able to evidence the damage and its costs. There may be some negotiation/discussion with the tenant (which should be written, or if oral, then summarised in an email after and confirmed by the other party), but if the tenant agrees, then that’s the deduction you can make.
If the tenant disagrees (which they may if you tried to ask for the whole cost of re-carpeting), then they can dispute the deduction with the deposit protection scheme. At that point, you be using the scheme’s Alternative Dispute Resolution (ADR) service and an adjudicator will apply the guidelines for what counts as wear and tear and how damage, like that to your carpet, is treated.
In cases like the carpet, there is some damage caused during the tenancy, but not enough to warrant the replacement of the whole carpet. The way they are likely to judge it therefore is like this.
They will, perhaps using evidence you submit (e.g. a receipt from when you had the carpet laid), find the cost of re-carpeting the room. They will judge how many years they expect a carpet to be in good condition before needing to be replaced, and how much the damage has accelerated that deterioration. They will then charge the full amount for replacing the carpet multiplied by percentage of life that the damage has accelerated.
E.g.
- cost of carpeting = £250
- average life span of a carpet before re-carpeting = 10 years
- amount of lifespan cut by the burns = 2 years
- Therefore, the deduction = £250 * (2/10) = £50
This is just an example of costs and lifespans, but this is the general logic that will be applied. The logic will only be applied in this manner if you end up using ADR, but the fact that this is how ADR works should be a material consideration during the fair treatment of a tenant when discussing deposit deductions.
Let me know any more Qs. I want to write up a detailed guide on this kind of thing soon, so knowing any outstanding questions would be very helpful!
Sam