Mid Position Valve changing Honeywell for Siemens how?

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Hi,

I have a small problem with the mid position valve fitted to our conventional heating system. The mechanism on top of the valve clicks when the central heating is switched on. In turn we get only hot water and no heat.

The motor inside is spinning but it seems the cogs underneath are just jumping rather than it changing position?

I presume a new valve is needed?

The current valve is a Honeywell V4073A however after searching today I could only get a Siemens 3PMP V22 from Wickes. The design of the new one is such that I will need to change the whole valve.

I'm fairly handy so have no real fears doing it myself, however I would like some direction on how to drain the system appropriately to change the valve over without getting a soaking. But at the same time I don't want to drain rads excessively unnecessarily.
 
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Have a look at FAQs 3 & 32.
If your existing Honeywell mid position valve has a dimple on the lid it would better to replace just the actuator than drain down system with all the problems you could get.
 
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We do these jobs by leting the system hang.

Bung the cold feed and open vent tape over any auto air vents open a drain cock, close it when water flow stops.

Now you can remove old valve and fit new one the water will sit in the pipes looking at you.

usually when going from one manufacturer of mid pos valve to another you have to remove olives and fit all new. You would be very lucky to be able to use existing nuts and olives.

I would have changed the head but you have your reasons for where you are now and have to make the most of it.

We use cone shaped purpose made rubber bungs but you could improvise. Someone here recommended denso.
 
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As a last resort, sometimes the valve gets stuck with gunk or for whatever reason. With the cover off and electrics off, try moving the metal arm that moves and engages the small micro switches. Spraying a suitable silicon type lubricating oil as you go. Be gentle, working it one way then back again, until its moves freely again. Make sure the oil has dried and evaporated before turning electrics back on. Worth a try before you get a new one.
 
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I have it switched to manual at the mo and the motor has started making a horrible noise.

I would have loved to have fitted a new head but I couldn't get one at the weekend, and can't be sure it's not a sticky valve that killed this one? I presume it's not to difficult to swap the olives? don't they just slip off and new slip on?

I'll fit the new one tomorrow with some luck.

Not sure on where you mean to bung to remove the need to drain down?

However I have bought some inhibitor so it won't hurt to do a drain and refill with fresh.

Am I right in presuming I can leave the hot water supply side alone? or would I have to drain that too?
 
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no you don't need to drain the dhw.

what you propose sounds fine.

but if i were you i would return the wicks valve & get a honeywell or preferably (imo) a horstman version (cheaper & better guarantee).

wait till monday & pop down partscenter.
 
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no you don't need to drain the dhw.

what you propose sounds fine.

but if i were you i would return the wicks valve & get a honeywell or preferably (imo) a horstman version (cheaper & better guarantee).

wait till monday & pop down partscenter.

Oh? are the Siemens ones no good then? I would rather get it sorted tomorrow if possible. This one cost enough money mind!
 
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as far as i recall they have the same wiring but do not have a removable head that is interchangeable with honeywell, which became the 'industry standard' 15 (guess) years ago.
 
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HOw to bung.

Unles you have a primatic cylinder in your loft thee is a large water storage tank with a float valve and a smaller one. The smaller one is your central heating feed and expansion tank.

Rising over and folding back down just through the lid is a 3/4" / 22mm copper pipe. Cap the end of it.

from the side or the underneath is a tank connector with a 1/2" / 15mm pipe this needs blocking.

We have a pair of rubber cones to block both pipes. The top pipe can be done with a 22mm (if it isn't 3/4") pushfit cap after having cut the rough edge off with a pipeslice. Then you just need to fashion a bung for the bottom tank connector.

Now you have a sealed system which once you have drained some water the rest will just sit there held by vacuum.

you must shut the drain off once the system is suspended.

Now you can undo all three nuts of the mid pos valve and replace it.

This will save a good few hous labour aswel as your chemicals, and avoids airlock problems when refilling.

Obviously remove both bungs on completion or you have made a bomb.
 
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Ah cool that makes sense.

I'll try that if I can find suitable bungs.

If not and I drain down how can I be sure the tank side has drained if I do it from one of the downstairs rads? Do I just need the valve I'm changing to be mid position or would I need to locate a drain on the boiler?
 

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