3 way valve of central heating system

most 3 way valves can be replaced by bunging the system meaning only a small amount of water is drained. it's about 60-90 minutes work. a full drain down is only required 1 out of 10 times

Good answer from Reliance. It may be worth noting that 3 way valves are generally found on older gravity based systems and as such are more prone to 'sludging up' etc. This therefore means that it generally takes longer to fix things. It is always a wise precaution to drain down a gravity fed system and clean out the F&E tank in attic before re-filling, add inhibitor, make sure the lid is securely on F&E is in place, etc. Take advantage of the 3 port valve change to get your system properly serviced and working well for winter.

Note your statement "i have cover with 24/7 for boiler and central heating" 3 port valve is part of your central heating. You need to check your contract and see if there is deuctable which is the same amount every time you had called them. There is cover for boiler only, plus central heating (which is radiators and pipe work), plumbing, electical. Like others have sugested you can ask how much extra would be to service your system for winter and add inhibitor. There shpuld be no extraIf you have cover for boiler and central heating with no deductable. This si ususally apx £20/month. If less then you probably have boiler cover only, if so £100 is reasonable

do not pay, drain down is part of labour and it may not need draining if head only change