No hot water through hot water tap - Water Heaters

Put that water in a glass and let it sit for a couple of hours. If it clears up, it is air bubbles. The old unit most likely had mineral deposits on the elements and they insulated the water from micro heating that creates the bubble. Since the unit is new, the water is in direct contact with the heating elements and micro bubbles are forming on the elements. When you turn the hot water on, the turbulence washes the bubbles out.

Combi-boiler-turn hot water tap on/off and the heating stops for ...

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Combi-boiler-turn hot water tap on/off and the heating stops for 20secs ... hot watertakes priority over central heating so when you run the hot tap, heating is ... Yeah onmy worcester combi there is a diverter valve - it feeds either the heating or ...

My central heating works but I have no hot water - 24'7 ...

https://www.247homerescue.co.uk/my-central-heating-works-but-i-have-...

Diverter valves switch heat between the hot water and the central heating. When youturn your hot tap on, the diverter valve temporarily shuts off the water supply ...

Does your boiler keep switching itself off? Here's why ...

www.dhs-uk.com/does-your-boiler-keep-switching-itself-off-heres-why/

Jul 7, 2015 - ... Bathroom Suites, - Showers, - Wet Rooms, - Taps and Accessories, Information and ... Low water pressure can cause your boiler to turn itself off. ... boiler is not turning off, you aren't getting the amount of hot water you require. ... If there is air in your central heating system, then your boiler may shut down.

Sounds like water leak.
For example, broken pipe... or water running out of TP valve.
That would explain variable hot-and-cold water at tap.
Turn off all taps, and observe if water meter is registering water usage.

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Were is the water boiler located.

This unit is set way too hot. The steam is pressuring the water out of the unit.

Oh some of these there was a small black heatexchanger just for hot water they some times block up . or it could be a blockage in the water section where it flows in .I know Valliant have a very good tech line and fitters who do house calls .

This on Y PLAN SYSTEM ???

He probably turned off the hot water at the water tank so that he could disassemble the faucet to repair it, then forgot to turn the water back on. If you have no water at all out of any hot-water tap, then you will find a closed water valve at the hot water tank. If you have hot water at all taps except the one he repaired, then you need to open the valve located under the sink.

You may need to replace the tap.hot water is causing the valve to expand and yours may be using a rubber seal inside which is causing expansion and hence no hot water is allowed through it..Trust me on that..

What is hot? Above 122F causes scald within 30 seconds. Get a temperature reading at tap. Use a candy thermometer if need be. If you want 140F water then your gas valve needs replacing.
In most code areas it is now illegal to deliver tap water over 125F to a consumer faucet.
You may love 140F but you jeopardize kids and Seniors.