Rent rebate is not based on whether or not a LL is “making an effort” to fix a problem. It’s to compensate the tenant for the lack of that service. I’m assuming they are unable to cook at home because they can’t use the sink therefore they’d probably have to get takeout. Compare the cost of a typical takeout meal vs home-cooked meal and you could see how it adds up over the course of 3 weeks.
You’re also assuming the LL is actually trying to fix the problem. They might just be looking for a plumber that could slap a temporary cheaper fix so the LL doesn’t have to spend money on fixing the root cause. You don’t know which of these two scenarios are at play here, and neither do I. The difference is, I’m willing to accept that the LL may legitimately be trying to solve the problem.
Having said that, in either cases, the tenant has to spend their money eating food outside, thus enabling rent rebate.
If you were my tenant, I’d tell you to pound sand.
If you were my LL, I’d drag your greedy ass to the LTB.