Replacing 3 port Mid-Position Valve

[wackyraces]

Could anybody help me out on how to change the 3 port mid-position valve MAV-322 (Landis & Gyr)? The valve has failed. I've replaced the motor but the microswitches have now failed. What brand / make shall I replace it with. I have a look at the Honeywell v4073. How do I drain the heating system to fit it? I have a standard heating system, Ideal Standard boiler and water tank in the cupboard. In the cupboard next to the tank is the pump and valve. The pump has 1 pipe going into the valve. The top of the tank has a pipe coming out, that then goes into the top of the valve and the bottom goes into the floor. The pump has a stop valve on it. The bottom of the tank has a pipe going in with a gate valve.

I hope that has described it! Any help much appreciated. Thanks.

 

[ollski]

Your best bet is to stick a hose pipe on one of the drain points on the radiator, turn off your water supply and drain it down to below the level of the valve. There are much quicker and easier ways without draining but it depends on your confidence and ability to put things right if it starts going titsup

 

[wackyraces]

Thanks for the reply. I'm not too bad at DIY, so if there is an easier way, could you describe what it is? I have all the tools and the wiring of the valve is quite straight forward.

 

[ollski]

Yep you buy a rad change bung kit which blocks the feed and vent in the f&e tank in the loft. Then you drain water from a rad or drain valve until it stops flowing, normally up to a pint or so. Shut that up and go and remove and swap over your valve while the water is held in the pipes due to a vacuum. If it starts glugging bang that new valve in as quick as you can or get wet.

 

[wackyraces]

Thanks for the help. I'll get a rad kit tomorrow. Hopefully I wont be swimming!!

Thanks for the top help.

 

[bster]

Make sure that you bung the correct tank!!!!!!!!!!!!!!!!!!!!!!!!

In my limited (extremly limited) experiance don't drain from a radiator then open the nuts on the valve, as you may induce air back into the circuit and water will flow again, drain the water from the valve that you are undoing until it 'holds' (stops).

 

[ollski]

Bster mate are you doing the rad valve back up before you take off the valve . Its a git to try and drain from the valve as it runs down the pipe and gets all messy. I must confess I have never had that problem you mention and I bung virtually everything.

 

[oilman]

............I bung virtually everything.

 

[namsag]

It is a 3 port valve so make sure you turn off pump valves and balancing valve on hot water return otherwise vacum wont be achieved.. As for bunging the right tank its amazing how flat a cylinder full of water will collapse to when done wrong.

 

[ollski]

............I bung virtually everything.

.......on the primary system, where possible, for the type of jobs I do etc etc

 

[wackyraces]

I think I will go for the long route round. Drain the system and then attempt it. The water tank collapsing doesn't sound good! Thanks to all for their advice.

 

[ollski]

It is a 3 port valve so make sure you turn off pump valves and balancing valve on hot water return.

Its amazing how many people say this, don't touch either next time namsag mate and see how you get on.