Key Takeaways
- Cold water always goes to the blue inlet, hot water leaves from the red outlet, getting this backwards is the leak I fix most often.
- Fit isolation valves on both lines so future servicing never means draining the whole flat.
- Use PTFE tape on threaded joints and a rubber washer on union nuts, never both on the same joint.
- Flexible braided hoses suit tight spaces, hard CPVC or copper suits long straight runs.
A geyser that heats perfectly can still ruin your week if the plumbing behind it weeps. Over the years I have been called back to more homes for a slow drip at the inlet nut than for any electrical fault. Good connections are quiet, dry, and easy to open again later. If you are fitting the whole unit from scratch, pair this with our water heater installation guide, then use this piece to get the pipework right.
Know Your Ports Before You Touch a Spanner
Every storage geyser has two ports under it. The maker colours them, but never trust the colour alone, always confirm with the booklet or the embossed arrows on the body.
- Inlet (blue): cold water enters here, and this is where the pressure and isolation valve sit.
- Outlet (red): hot water leaves here and travels to your taps and shower.
Reverse these two and the tank fills but the hot water sits trapped, so you get a trickle at best. It is a five minute mistake that costs an hour to undo.
Choosing the Right Pipe Material
The pipe you pick changes how long the job lasts and how easy the next repair is. There is no single best answer, it depends on your run and your budget.
| Material | Best for | Watch out for |
|---|---|---|
| Braided flexible hose | Tight gaps, quick swaps | Ages in 4-5 years, check yearly |
| CPVC | Long runs, hot lines | Needs solvent cement and cure time |
| Copper | High heat, long life | Costlier, needs soldering skill |
| PPR | Concealed piping | Requires a fusion welding tool |
For most flats I use two short braided hoses at the geyser and hard CPVC for the run to the taps. It gives easy service at the unit and a solid line in the wall.
Sealing Joints the Way That Holds
A joint leaks for one of two reasons, poor sealing or over tightening that cracks the thread. Both are avoidable.
- Clean the male thread so no old tape or grit remains.
- Wrap PTFE tape in the direction the nut turns, four to six firm turns.
- Press the tape into the threads with your thumb so it does not unravel.
- Start the nut by hand for two full turns to be sure it is not cross threaded.
- Tighten with a spanner, then stop at a quarter turn past hand tight.
- Wipe the joint dry and watch it under pressure for five minutes.
Warning: Do not use PTFE tape and a rubber washer on the same union joint. The washer alone seals the flat face, extra tape holds it apart and creates the very leak you were trying to prevent.
Fitting Isolation Valves
An isolation valve on each line is the small part that saves you the most trouble later. Shut one and you can open the geyser without draining the building tank.
Put a valve on the cold inlet at minimum. Many good installers add one on the hot outlet too, so the whole unit can be dropped for a swap in ten minutes. Choose full bore brass valves, the cheap plastic ones seize within a year in hard water. The electrical side matters just as much, and our electric geyser installation walkthrough covers the wiring that pairs with this plumbing.
The Pressure Relief Connection
Storage geysers build pressure as water heats and expands. The pressure relief valve, or multi function valve, sits on the inlet and lets a little water escape when pressure climbs. This is a safety part, not an optional extra.
- Point the relief outlet down toward the drain, never up or at a wall.
- Expect a few drops during heating, that is the valve doing its job.
- A steady stream means a stuck valve or high mains pressure, address it, do not plug it.
You can read the general principle behind these devices on the relief valve reference page, but always fit the exact part the maker supplies.
Testing and Bleeding the Line
Before you power the geyser, the tank must be full and the air pushed out. Firing a half empty tank cooks the element.
- Open the inlet isolation valve fully.
- Open a hot tap downstairs or nearby and wait for air to sputter out.
- When a steady stream runs with no bubbles, the tank is full.
- Close the tap, walk every joint, and dry each one with a cloth.
- Only now switch on the power and let it heat.
Tip: Keep a torch and a dry tissue in the bathroom cupboard. A tissue pressed to a joint shows a slow weep long before your eye catches the drip on the floor.
If you would rather work from a printed sequence, the geyser installation checklist lists every plumbing check in order.
Frequently Asked Questions
Which port is the inlet on a geyser?
The cold water inlet is usually marked blue and carries the pressure and isolation valves. The hot outlet is marked red. Always confirm with the arrows embossed on the body or the maker booklet, since a reversed connection gives almost no hot water.
Can I use flexible hoses instead of hard pipe?
Yes, braided flexible hoses are fine and ideal in tight spaces where a rigid pipe will not bend. They do age faster, so check them once a year for bulges or rust at the nut and replace them every four to five years to stay safe.
How much PTFE tape should I use on a joint?
Four to six firm turns in the direction the nut tightens is enough for most geyser threads. Press it into the grooves with your thumb. Too little leaks, too much stops the nut seating fully and cracks the fitting under pressure.
Why does my geyser drip from the relief valve?
A few drops while the water heats is normal expansion being released. A constant stream points to high mains pressure or a stuck valve. Fit a pressure reducing valve if your mains is strong, and never plug the relief outlet to stop it.
Do I need an isolation valve on the hot side too?
You must have one on the cold inlet. Adding a second on the hot outlet is not compulsory but makes servicing far easier, letting you remove the geyser without draining downstream pipes. Use brass full bore valves so they do not seize.
Pipework You Can Forget About
The best plumbing is the kind you never think about again. Get the ports right, seal each joint with care, fit good brass valves, and your geyser will run dry and trouble free for years. For the wider setup and more room by room advice, visit our installation section or return to the main water heater installation guide whenever you plan your next job.
