Draining down Rads to fit new 3 way Motor Valve

[gunnag]

Hi All,

the three way valve in my central heating/hot water system has failed so I'm now planning on replacing the entire valve and motor unit.

This is probably the 4th time I've changed it in the 20 years I've lived in the house. The current Siemens 3PMP-V22 has lasted over 7 years but I've forgotten how I fitted it, hence I need some advice here.

There is already an Adey Mangefine filter fitted and to help clean the system for the new 3 way valve, I added 500ml of Adey MC3+ Rapide yesterday. I flipped the 3 way valve manual lever to ensure I have some heating and HW for now whist the cleaner circulates.

The 3 way valve, Magnefine filter, HW tank & pump are all located upstairs in the airing cupboard.

The next step is to drain the radiators, my plan is to turn off the isolation valve on the heating header tank feed in the loft, then connect a hosepipe to the downstairs radiator stopcock and open it. This should empty the rads of water and cleaner.

Once empty I should be able to unbolt the 3 way valve, noting its wiring and simply bolt in the new one and rewire. The new valve is a Drayton MAI/678-3, I note that if this goes wrong the motor can be removed and replaced separately from the valve.

My main worry is whether I need to drain the hot water from the tank? For some reason I have it in my head that I did this once before and it caused all kinds of problems, perhaps it was another project & logically I cant see why I would need to drain the HW.

One the rads are refilled I will use inhibitor to help prevent rust etc.

Does this sound right?

All info welcome.

 

[denso13]

My main worry is whether I need to drain the hot water from the tank?

No, no need to do that.

 

[terryplumb]

You don't need to empty the HW cylinder.

 

[gunnag]

Thanks for confirming, I will leave the HW well alone.

 

[oldbuffer]

1. As said above no need to drain hot water cylinder.
2. You will only need to drain the whole system to get rid of the cleaner. If there was no cleaner in there you would only need to drain down to (just below) the level of the motorised valve.
3. I'd suggest emptying and cleaning out your F&E tank after isolating water to it but before draining down. If you just drain down, any sludge / muck in the F&E will go into your system.
4. When you add the inhibitor make sure it goes into the system. Just emptying the chemical into the F&E tank won't necessarily do that.

 

[gunnag]

Good tip, I will clean out the header tank first, before refilling, I usually add the inhibitor to the Magnefine cylinder which I believe is OK.

 

[gunnag]

All done, well almost done, I isolated the header tank, cleaned the tank, drained the system and then I swapped out the 3 way valve complete with wiring.

The header tank was completely full of muck, luckily the exit hole was on the side so I don't think too much could get into the system.

When I turned the isolator tap back on, there was nothing, no water at all. I checked the cistern valve and thats OK, so looks like the isolator tap is broken.

Just been to Screwfix to get a new isolator tap, its 15mm with compression joints each end. Anyone know if I can get away with reusing the old olives assuming the nut threads are the same ?

 

[denso13]

Anyone know if I can get away with reusing the old olives assuming the nut threads are the same ?

Yea, that's fine.

 

[terryplumb]

Is it a gate valve ,big red ,round wheel head ? Pure junk !!
Very good chance existing nuts and olives can be re used. Smearing LSX on the olives is advisable.

 

[ianmcd]

good chance they will be the same, if not just cut the olives off, not a big job

 

[gunnag]

It wasn't a gate valve with the red handle, it was in-line type where a flat bladed screwdriver is needed to turn it on/off. Guess I must have broken something internally, luckily in the shut position.

I was worried the new isolator wouldn't fit as the threads might be different, but I think it will be OK now, will try fitting in the morning and report back.

 

[terryplumb]

Where is this valve situated ? Unusual for a ballofix type valve to fail in the manner you outlined.

 

[gunnag]

The isolation valve is in the loft supplying the header tank and float valve, I undid the compression joint between the isolation valve and float valve to check the flow, and there was no flow regardless of which way I turned the 'flat', so it looks like the isolation valve is stuck closed, maybe the shaft has sheared?

The CH header tank and larger cold water tank are both supplied by the same feed with the CH header being tee'd off first for its own supply. The cold water tank still works perfectly so it doesn't seem to be a supply issue.

 

[old duffer]

place isolation values either side of the valve...you know you will have to replace the valve again in a few years so make life easier for yourself.

 

[gunnag]

All sorted now, fitted new isolation valve in place of the old one, threads were the same so just screwed on.

Had some issues with air locks which caused the boiler to lock out from overheating.

Needed to drain water from 5 downstairs radiators using the stopcock. Despite attaching a hose to the spigot and using a jubilee clip, water seemed to pour through the valve and go everywhere. Is there an O ring or something to stop this?

I don't know why each of the downstairs radiators has a stopcock, maybe I've just got a weird layout.

Anyway all working now.