My dear this is your tooth senstivity issue . Not directly linked with the RCT . . Most probably caused by your inappropriate brushing style and hard abrasive dental paste or powder . Hot and cold brings you sharp pain that's more likely a sharp sensation of nerve endings opening to environment. If hot sensations  is more then you need to be quick as possible for not getting more close to RCT.  Kindly provide the area where you feel the sensitivity , is at the junction of tooth and gum line?

An x Ray would clearly suggest what should be your further steps !! Initially sensitivity will start which would last for five secs and in later stages , as weather changes these sensations increase! When sensations become intolerant, immediately go for RCT, it seems you wouldn't want to go for treatment as of now. Try to have food which is just warm.

Sensitivity to hot food means it is infected till the nerves of the tooth.But to diagnose it perfectly there is need of dental X-ray.

It should be clear by x ray only ...if the teeth is carious get it restored ur prblm wil be solved nd u can also use some desensitized paste after consulting ....further still if it is not cured then go fr rct ..