draining down / refiling a systems boiler?

[bythesea]

hi
im going to change a trv tomorrow and dont want to do it live
just a bit worried though as its a systems boiler?
usually on a pressurized system id drain it down and refill the pressure via the filling loop
but this doesnt have that just just a gas feed in and a blow off pipe. theres a cylinder upstairs with a 3 way valve and im presuming a feed and expansion tank in loft topping up system?
it seems to top itself up as when i empty the rad there is plenty of water to push back through
just wondering the best way to go about it
cheers

 

[lame plumber]

use a plumber, your out of your depth, watch him do it and then youll have an idea next time

 

[Rybo_1]

Won't have an f&e tank if it's a system boiler

 

[bythesea]

Won't have an f&e tank if it's a system boiler

Maybe I have te terminology wrong can anybody help ?
I thought there would be a tank above the cylinder feeding it ?
i thought it was a systems boiler as there is only 2 pipes going in . I'm pretty sure it's a vented system as I say u can't top the system up . Not like you would on a pressurized cOmbi . So would I isolate the tank above and hae to drain down the whole cylinder just to change a compression try is there a better way ?

 

[Rybo_1]

Sounds like you have a vented heating system. You won't need to touch the cylinder at all for this.
Turn heating controls off, start draining system, pop up in loft, check small f&e tank is filling. If it is then isolate it. Open up all vents on upstairs rads, after a few minutes. Do your work, do all pins up, reinstate f&e tank. Check that it's coming through drain off, if yes, shut drain off. Check your work and then bleed all rads. Turn controls back on and heat test

 

[Ermintrude]

Don't forget to add inhibitor to the empty tank

 

[Rybo_1]

Ooooops and that!