How do i turn off hot water supply from this boiler, need to change bath hot tap valve

At the boiler should be a purge setup. This consists of a valve to shut the zone off, and downstream of that valve is a drain ****. Attach a hose to the drain ****, and with the boiler running, close the valve and open the drain ****. (Turn the heat up on one zone at a time if you have multiple zones.) You should be able to notice when the air comes out of the hose by hearing it and the hose twitches and jumps when large amounts of air come out. After the air stops coming out, open the valve , close the drain, flip the bypass closed, and let the water circulate, then reapeat procedure. Do this until you hear or see no more air. You can run a long hose outside or you can use a bucket and a short hose. Using the bucket allows you to actually see the bubbles of air, but you will be dumping many buckets before you are done. Most boiler feed valves have a fast fill lever that bypasses the slow 12 psi that the boiler is normally fed at. Using this will speed up the purge considerably, but don't forget to flip the lever back down between, and after purging or the boiler relief valve will blow off and make a mess. Good luck!

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.

Boilers are inherently dangerous for the average DIY for so many reasons, contact British Gas and have them come back and fix it, tell them it was fine before the "service". They may simply have a control valve shut off.

If no hot water it is the diverter valve in the boiler. If no cold water the tap in the mains water supply to the boiler may be turned off

Check for crossover.
Bad check valve.
http://waterheatertimer.org/Crossover.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

clicking rads are due to pipe expansion when getting hot.
If the hot water [secondary circuit] gets hot and the boiler stays on [does not keep going on and off] even with a constant low water flow then the diverter should be ok.
there is a valve to prevent the primary circuit [central heating] [ CH] from sending water to the rads. this or its control may be at fault.
both the
Both the CH pipes to & from the boiler should have manual valves to turn off. do this then try the hot tap-full on. If the boiler goes into overheat mode and the overheat stat kicks in to turn the boiler off -- then :-
Check also the heat exchanger, it may be furred up especially if you are in a hard water area. It means taking it off and manually checking [pour water through] If you're lucky it will be just muck to be forced out with hose pipe pressure, if not a new one

most likely the diverter valve.. when hot tap turned on the movement of the water through the valve operates a diaphragm which pushes a pin/button//switch to tell the boiler to fire up

water must be set at 3lts a min ,check diaphragm valve move when hot tap is on, check microswitch ,best of luck

mixing valve must be replaced

baxi boiler relief valve blows off when heat is turned on when hot water is working it is fine