Plumbing.... how hard can it be?

I’ve never been mechanically minded, but when a tap knob recently fell off I thought I’d go one step further and change the whole thing since it wasn’t that great to start with. Looks simple enough, unscrew, remove, fit new, rescrew. Not sure google is the best guide but I’ve got all the bits and am about to attack it.

What I’m not sure about it how to do a hot tap? I’m confused as to what flows where. House has a water tank in the loft. One pipe going in to fill, one out near the bottom. Under it in room below is a hot water cylinder.

A pipe out of the top feels warm to the touch and I guess is where the hot water comes out. It goes to a T and one branch goes behind the cylinder where I can’t see anything, the other goes into the ceiling to unknown. On the lower end of the cylinder are two pipes which are both warmer to the touch. I presume they loop to the gas heater in kitchen. A larger diameter pipe is also there, with a stopcock on it, and it feels cold to the touch. I assume that’s where cold water comes in.

Beyond that I’m clueless. If I stop water going in, does that stop water going out? Or worst case do I need to drain the whole hot water system to change a tap?

One step at a time, I’ll have a go on the cold tap first. If you hear reports of flooding in Wiltshire on the news, then you’ll know the probable cause.

In the ill fated words from Top Gear: “How hard can it be?”

I give up. Couldn’t shift the nut holding the cold tap on and the pipes were really bending under the force. Afraid I’ll break something and really stuff it all up. Time to find and give someone else a ton of cash and get it done properly… anyone want some plumbing gear? Used once or less.

My father in law was a plumber and helped me do lot of re-plumbing in my house teaching as we went - 0ne thing he kept saying was - " most houses are like xxxxx but there is always a different way of doing things" having said that - your presumptions are correct - the hot T junction supplies the hot water taps in the house and the one that goes into the roof should come up next to the water tank and over the side finishing above the water - overflow for safety in case the hot water boils for any reason - switch of the water coming into the hot water tank and turn on all the hot water taps in the house, they should stop flowing in just a few seconds - removing the taps may still cause some water to spill, but is easily contained with an old towel or two - if you are just changing the valve barrel it is as simple as you say - but if you are changing the whole tap beware - there are some really simple traps to fall into - not all taps have the same fittings or have the same length stems - don’t force the existing pipe run to fit - guaranteed leaks, as is re using the old olive (the domed brass ring on the pipe that forms the seal, they are strictly single use items), buy or scrounge some ’ plumbers mate’ or similar sealing compound and use it sparingly around the new olive before assembling the joint - DO NOT over tighten the gland nut (snug + 1/2 flat max, a little more if it seeps ) .

Edit - got distracted whist typing my contribution so failed to see your last post - don’t give up - restrain the tap body using a Stillson or similar padded with rag whilst using a proper spanner to undo the nut - no adjustable wrenches unless you want a rounded nut .

It was the whole tap I was going to change. It wasn’t great but still worked before then other than the knob falling off (inside plastic bit worn away). Did consider a bigger spanner but the set I have didn’t go that big. If I’m mad enough to try again I can borrow one from work.

Looking back, I wasn’t that great with DIY watercooling either!

Tomorrow I’m doing something safer. Painting. Even I can’t get that wrong…

A much easier option is to buy a tap kit, not very stylish but very easy to fit, and within the scope of any DIYer and available in most DIY stores. just leave the body in place and replace the brass bits - they don’t stick quite so hard.