Key Takeaways
- An instant geyser heats water only while the tap runs, so mounting height and pipe length decide how quickly hot water reaches you.
- Fix the unit on a solid wall with proper wall plugs, keep it clear of the shower spray, and use a dedicated 16A point with earthing.
- Most 3 litre models cost ₹2,500 to ₹5,000 and take a careful person 60 to 90 minutes to fit.
- Never skip the ELCB or RCCB and the earth wire, a wet bathroom leaves no room for a shortcut.
An instant water heater, what most families here call a tankless or 3 litre geyser, is the quickest hot water fix for a kitchen sink or a single bathroom. I have fitted dozens of them in flats where a big storage tank simply would not fit. If you want the full picture on any type of unit, our guide to water heater installation sets the ground rules, and this piece narrows it down to the instant model.
How an Instant Geyser Behaves
There is no tank sitting full of hot water. A heating element switches on the moment water flows through the small body, usually 3 kW to 4.5 kW of power drawing hard on your wiring. That is why the electrical point matters as much as the plumbing.
Because it heats on demand, you get warm water for as long as the tap stays open, but only a thin stream at a comfortable temperature. Open the tap too wide and the water runs cool. I always tell families this before I fit one, so nobody is surprised on the first winter morning.
Tools and Parts to Keep Ready
Lay everything out before you touch the wall. Half the delays I see come from a missing wall plug or the wrong size spanner.
- Electric drill with a masonry bit, plus wall plugs and screws (many come in the box)
- Two adjustable spanners and a pipe wrench
- Teflon (PTFE) thread tape for every threaded joint
- Two flexible connection hoses, inlet and outlet, rated for hot water
- A spirit level, a measuring tape, and a pencil
- Tester screwdriver and insulated pliers for the wiring
Choosing the Right Spot on the Wall
Position decides everything about daily comfort. Fix it close to the tap it serves so hot water arrives fast and little heat is lost in the pipe run.
- Mount it above and to the side of the outlet, never directly in the shower spray zone.
- Keep the body at least 1.8 m off a wet floor so nobody brushes it with a wet hand.
- Leave 150 mm of clear space around the unit for the pipes and future servicing.
- Pick a solid brick or concrete wall, not a hollow partition that cannot hold the weight when full.
Mounting the Unit Step by Step
Turn off the bathroom circuit at the MCB before you start drilling anywhere near old wiring. Here is the order I follow on every job.
- Hold the mounting bracket against the wall, check it with the spirit level, and mark the two hole positions.
- Drill the holes, tap in the wall plugs, and screw the bracket tight so it does not shift.
- Hang the geyser on the bracket and give it a firm tug to confirm it is seated.
- Wrap Teflon tape clockwise on the inlet and outlet threads, four to five turns each.
- Connect the flexible hoses, inlet to the cold supply and outlet to the tap side, hand tight then a quarter turn with the spanner.
- Do the wiring last, once the plumbing is done and dry.
Plumbing the Inlet and Outlet
The two ports are marked, usually blue for cold inlet and red for hot outlet. Getting these reversed is the single most common mistake, and it leaves you with no hot water at all.
Fit a small isolation valve on the inlet so you can shut the water for future service without draining the whole house line. Do not over tighten brass fittings, a cracked thread will weep for months before you find it.
Warning: Never switch an instant geyser on before water is flowing through it. Dry firing burns the element in seconds and voids the warranty. Fill the line and let water run from the outlet first.
Wiring It Safely
A 4.5 kW unit pulls close to 20 amps, so it needs a proper heavy point, not a shared 6A socket. Use a dedicated line with 2.5 sq mm or 4 sq mm copper wire depending on the load, feeding through its own MCB.
The earth wire is not optional. In a bathroom, an ELCB or RCCB on that circuit is what stands between a small leak and a real shock. The wiring principles are the same across models, and our walkthrough for installing an electric geyser covers the electrical side in more depth. For the national picture on efficient appliances, the Bureau of Energy Efficiency is a good reference.
Testing Before First Use
Do not rush this part. A calm ten minutes of checking saves a soaked ceiling below.
| Check | What to look for | If it fails |
|---|---|---|
| Water joints | No drip at inlet or outlet after 5 minutes | Re-tape and re-tighten the weeping joint |
| Earthing | Tester shows no leakage on the body | Switch off, recheck the earth connection |
| Heating | Warm water within 20-30 seconds of flow | Confirm inlet and outlet are not swapped |
| ELCB trip | Trips on the test button | Replace the faulty ELCB before use |
Run the tap for a full minute, feel the pipe for any warmth in the wrong place, and only then call the job done. If you like a printed list to tick off, the geyser installation checklist is handy to keep in the bathroom cupboard.
Tip: In a hard water area, fit a small inline filter on the inlet. It keeps scale off the tiny element and adds a year or two to the life of the unit.
Frequently Asked Questions
Can I install an instant geyser myself?
You can do the mounting and plumbing if you are careful and handy. The electrical connection, with its dedicated point, earthing, and ELCB, is best left to a licensed electrician. A wet bathroom is not the place to learn wiring by trial and error.
What size instant geyser do I need?
A 3 litre unit suits a single tap or basin for handwashing and shaving. For a bucket bath you may wait a while, so a small 6 litre or 10 litre storage geyser often serves better. Match the model to how you actually use hot water.
How high should the geyser be mounted?
Keep the body at least 1.8 m above a wet floor and out of the direct shower spray. High enough that nobody touches it with a wet hand, low enough that the pipe run to the tap stays short so hot water arrives quickly.
Why is my instant geyser giving lukewarm water?
Usually the flow is too high for the element to keep up. Close the tap slightly and the temperature rises. If it stays cold, check that the inlet and outlet were not swapped during fitting, a very common installation error.
Does an instant geyser need a pressure valve?
Most instant units are open outlet and do not build pressure like a storage tank, so they rarely need a separate safety valve. Always follow the maker booklet, since a few pressure type models do require one on the outlet.
Getting Warm Water Flowing With Confidence
Fitting an instant geyser is a satisfying afternoon job when you respect the wall, the water, and the wiring in that order. Take your time on the earthing and the joint tape, and the unit will serve quietly for years. When you are ready to plan the wider setup, browse more guides in our installation section or start with the full water heater installation guide.
