hot water

[FRANKIEJUNIOR]

i went to fix a relatives dripping mixer tap in the kitchen thinking this will be easy, especially when she told me all i had to do was fit a new valve inside it that she had already bought. As it was the hot side that was dripping, all i had to do was turn the hot water off. However there were no service valves underneath the sink,and when i asked her to show me the hot water cylinder to turn the cold feed off from the c.w.s.t she showed me a gas combi boiler instead.
The make of the boiler was primus and i was able to identify gas and
central heating flow and return and cold mains in with filling loop into return. there was no service valve on the 15 mm domestic hot water pipe however. Do i turn the mains valve off? I didnt think i could do that as i thought the boiler needs the water flowing through it to protect the heat exchanger unless you turn the boiler off first, and she didnt want to do that. should there not be a service valve fitted on this pipe near its connection to the boiler,as there was a gate valve fitted on the c.h flow for some reason. Can anyone tell me how to isolate the tap to fix a simple but now complicated job.

 

[tomy]

if there is no service valve on the cold feed into the boiler turn off the cold at the mains , open the hot tap , change the valve , turn on water again .

 

[FRANKIEJUNIOR]

if there is no service valve on the cold feed into the boiler turn off the cold at the mains , open the hot tap , change the valve , turn on water again .

There is a blue lever valve on the cold feed into the boiler yes,but i was afraid to turn it off as i thought the boiler needed water flowing through it, and therefore you needed to isolate hot water on outlet end after its passed through boiler. thank u for putting me straight however out of curiosity why would a gate valve be fitted on the c.h flow pipe. would it be to isolate and drain the boiler. thanks again.