Hot water only comes on when numerous taps are running

[CrazeUK]

Hi Guys.
I have a Baxi 105 HE.
We have an issue where the boiler doesn't come on for the hot water.
It does come on when you turn both the basin and bath taps on to full flow.

I assume there is a flow valve/switch that detects when the water is flowing.

My questions are:
1. Where is it on the boiler?
2. Can it be fixed by me (I am having the full central heating system looked at and probably replaced in about a month.
3. How much would it cost for parts and labor if I was to get it done by someone?
4. Is it safe for me to change my self (as I am not messing with gas components?

Thanks in advance

 

[gas112]

search for diaphragm and venturi on this site and there is numerous explanations on how to repair its a realtively simple repair if your mechanically minded both parts 15 quid each max.
nothing to do with gas so ok to do

 

[TargetDummy]

I had exactly the same problem. It was the venturi. £15 for a new one and 5 minutes with a spanner and it's back to normal

[GALLERY=media, 102824]20190406_145347 by TargetDummy posted 10 May 2019 at 6:55 PM[/GALLERY]

This is the broken venturi I replaced. Remove yours and see if it's still in one piece

 

[gas112]

and you managed to fish the spring out target they can be a nuisance to get out

 

[TargetDummy]

Yeah, couldn't find the top part of the cage though...