My radiators arent switching off properly so are always on. British Gas sent round a service man who said the 3 way valve on my boiler needs changing, and this will cost £250 in man hours. Hes got to drain the system, replace the 3 way valve then refill the system. Can I save some money and do it myself or is it a job for a professional?

Matt Cartmell, May 2004

Another way to change the valve is by `bunging the system`..This saves time and reduces airlocking problems and there`s no need to re-inhibit the system.It can be done in about 15-20 minutes.The downside is that there`s a small chance that the bungs could fail causing a leak (however in 10 years of plumbing this hasn`t yet happened to me).You can buy these bungs in most plumbing shops and they`re specifically designed for this type of work.
Firstly isolate the the c/h system at the fused spur and remove the 3 amp fuse.Next go into the loft with your bungs at the f/e tank and push one into the open vent (pipe hanging over tank) and one into the cold feed (pipe exiting the tank at the bottom).Make sure there`re tightly in place..Tighten up any auto air vents on the system/top of boiler.
Next go to the 3 port valve and get some towels/absorbant sheets and a tray if you can get one in and place.Cover up any electrical parts..Depending on the type of valve you may be able to move the actuator head exposing the body which makes it easier..
Carefully undo one of the nuts securing the valve to the pipe work but only enough for water to start flowing from the joint.Collect the water in your tray
and be patient as it may take a few minutes.When the water stops flowing undo the other nuts and drain in the same way if any water flows.
When the water has stopped flowing, the bungs have created a vacume and you can remove the valve and replace with the new one..Don`t bother changing the nuts and olives unless they don`t fit..Obviously you don`t want to take ages over this or wander off to make a cup of tea with the valve out as if one of the bungs failed you`d first hear a gurgling noise followed by lots of water..Use plumbers mate/ptfe on the threads and tighten up..
Once tight go back into the loft remove the bungs, go back to the valve and check for leaks..Loosen off the auto air vents and bleed any air out of the system.Turn on the h/w,c/h and check it`s all working.
Jobs a goodun !!

stupot, June 2009

Here's what you need to do:-

Buy the replacement valve [these usually retail at about £30-£40].

-Turn the boiler off.
-Turn the water off to the header tank to stop it refilling [assuming it's an open-vented system here by the way].
-drain down the system as far as is needed to empty the 3-port valve - hopefully there will be a drain-cock at a low-point.
-if the valve is of the normal variety, it will be a plastic motor attached to the metal valve section. You should be able to detach the one from the other.
-Assuming the valve is the buggered bit, undo the three compression fittings holding the valve in place- the nuts will probably have to stay on the pipe as an olives will be stuck in place..
-Pop it off and wack your replacement part in there. I always use PTFE tape no matter what the job - do them up nice and tight.
-Refill the system with water and then re-drain it - you should probably dothis a couple of times, to fluch out any debris].
-When refilling the final time, include a pack of inhibitor, to protect against corrosion.
-Bleed your radiators.

Bob's yer uncle!

John Banhsee, November 2004

You will need experience with making joints with copper pipe
and some electrical work. If you have these skills then the job
can be done quite easily. The system will need to be partly
drained before starting the work.

Jason, October 2004