Help me fix my dripping tap please!

[WaterMess]

Bathroom tap is dripping. My extensive googling shows I probably need to replace the washer. I have a multipack of washers and the tools needed but I need some help on how to turn off the water. There is no visible isolation valve on the pipe leading to the dripping tap. I have an immersion heater with a water tank above it. Is there a way of just turning off the water coming from the immersion tank rather than having to turn the main stopcock off and then draining the whole massive water tank above?

Any plumbing experts (or just people with more diy knowledge than me!) out there? Really would love to avoid flooding the place.

Watching as I too have a leaky tap and a dripping shower and a plumber who has left me on the read !

beginning to think it’s time I learned DIY

Google tells me that dripping taps should be a very easy DIY task... Once I can get the water turned off 😬We can do this!!

This

Sorry, didn't read all your post! I used one of these on my kitchen sink. Not sure if it's the same for the bathroom

My water isolation is under the kitchen sink

You need to turn water off at mains and drain system before unscrewing tap to replace washer.

It's the hot tap dripping is it?

Thanks for the replies, I was hoping to avoid draining the whole tank but will do if necessary, obviously.

Yes @pigsinoodies it's the hot tap, bathroom sink.

There may (should) be a valve on the feed pipe to the water tank. If you shut that off it stops the tank from refilling and you can drain the system as much as you need to by running the tap you're working in.

Don't forget to turn the immersion heater off.

On the feed pipe to the hot water cylinder that is, not the tank in the loft.

There should be a gate valve (usually round, red tap) on the hot water supply FROM the immersion tank) so you don't need to drain it down.

Hot water feed is the pipe coming out of the top of the tank, if there is no valve you'll have to close the cold feed to the tank.
First turn off the heater element (should be a lighted switch, just follow the cable if it's not obvious).
Cold feed gate valve is usually near the tank but sometimes near the header tank.
In extremes if you can't find any valve to shut off the cold feed you can tie up the ball valve in the header tank.
After fixing the tap and refilling make sure you have running water from the hot tap before switch tank heater element back on.

Good luck

Modernish bathrooms should have isolation valves or taps under the sink or kicking piece if your stuff is built into furniture