As per the title, this involves a deficiency with said zone valve, namely the relatively common issue of heat leakage into the radiator circuit when calling only for hot water.
It's been a 'quirk' of the system for the past few years (possibly the past decade... or so). Regarding this problem as merely a 'quirk' arises out of the fact that, rather conveniently, the first floor rads only get very warm as opposed to hot with the ground floor rads remaining stone cold (or just slightly warm) and I'm assuming the 2nd floor rads must be getting some heat but two out of the three have been shut off via their TRV heads so no great loss, especially in the cooler seasons (Winter, Spring *and* Autumn - most of the year, here in Blighty).
The 'uncalled' heat to the first floor rads is rather useful in that whenever we need a bathful or two of hot water in our first floor bathroom, the adjacent bedroom(s) and landing, as well as the bathroom, get the benefit of this 'wasted' energy to remove the chill and provide heating for the towels draped over the rad(s).
However, SWMBI's complaints over the past few years of the rads getting warm when only hot water has been called for, were finally wearing me down so, with the promised heatwave and continuing warm period being forecast by the met office a couple of weeks back, I finally steeled myself to the task of "mending the problem" earlier this week (not the slack jawed response, "I must go out and spend 70 to 150 quid on a complete replacement 3 port valve so I can do a swift swap out regardless of how fixable said valve might turn out to be.").
I part drained the system down (crystal clear fernox/water mix) sufficiently to allow me to remove the valve assembly from the airing cupboard plumbing on the half landing just below the first floor where the hot water tank and the CH pump reside (the boiler, a floor standing Ideal Mexico Super 100, resides in the basement).
The valve location makes working on the motor head assembly extremely awkward to say the least, and being the earlier version of the V4073A (did I mention it was 30 years old?), I knew there was no mileage in assuming there'd be the remotest possibility of being able to swap out the motor head without a part drain down regardless.
It was at this point that my futile efforts at undoing the A and B Compression joints (28 and 22 mm pipework respectively) reminded me that I'd previously tried to tackle the problem in a prior year (the vagueness of my recollection - more a sense of de ja vue really, suggests this could have been several years earlier). I'd managed to slacken the AB 28mm compression joint with only a level of difficulty just this side of insurmountable.
What I was lacking was an open ended 1 1/2 inch (38mm) AF spanner or adjustable wrench that could open its jaws to that distance (the largest such wrench I had was marked as "300 mm" (aka 12 inch handle) which only opened out to 36mm AF. There seems to be a shyness about indicating the maximum AF dimension, possibly based on sound engineering practice that you could calculate the maximum AF size any sane tool designer would choose to go with any particular handle length - in my case, I guess a 15 inch wrench would be what was required (jaw width to handle length ratio of 12% seemingly being the perceived wisdom amongst sane designers of quality adjustable wrenches).
I only mention this after looking at a 12 inch adjustable in B&Q that was *calibrated!* to a 42mm jaw opening with an extra 2 or 3mm to spare and wisely reconsidered the RoI on a tool with a 15% jaw width to handle length ratio priced at 16 quid. If they'd had a 15 inch wrench based on the 12% design rule at that price, I'd have bought it, no hesitation.
As it turned out, I'd made a *very* wise choice when I dropped into a local second hand tool shop, on our journey home (which my SWMBI had wrongly assumed was no longer in business on account of the fact that most of the other shops in that road had disappeared). Hint to the wise, trust your own instincts and verify for yourself any bad news offered by your other half in regard of such matters.
Within 2 minutes of entering said emporium (including 90 seconds of swift banter with the proprietor before asking the important question), I'd dug out the required 1 1/2 inch AF open ended spanner from the box I'd been directed to.
Normally, in such emporia, I'd try to haggle the price down, no matter how low it was to begin with. In this case, I felt it would be just a little bit churlish of me to haggle over his 4 quid asking price considering the fiver's worth of unleaded me and the XYL had already squandered in a fruitless trip to a market where the Sunday tool stall magically becomes something else in mid-week and the not so local Aldi nearby whilst *still* having stock of a Jumbo Spanner set for a reasonable £29.99, turns out to be not quite so 'jumbo sized' as I'd hoped (it maxed out at a rather pathetic 32mm AF open ender).
All in all, I emerged from that shop, spanner triumphantly in hand, after just 5 minutes. I usually have a good browse around such places for half an hour or so looking for other 'interesting bargains' but, in this case, I wanted to particularly make a point to my XYL so kept the transaction uncharacteristically short.
Suitably armed, I was able to set to, to do battle once more with that recalcitrant zone valve without undue risk of co-lateral damage to the surrounding plumbing and liberate my prize.
Examination revealed, as anticipated, that it was the older design which required a drain down even for a motor head swap out. It also revealed that it was the more useful valve body design with 1 inch bsp fittings on all three ports allowing the use of 28mm compression joint adapters without the restriction of the newer 22mm compression joint only valve body (only the HW B port was fitted with a 22mm compression joint adapter in my case).
I noticed that all the cheap 48 to 70 quid on-line supplier priced versions of the V4073A referred only to 22mm compression joint fitting options (a problem when it comes to coupling up to 28mm pipework, even assuming you're prepared to accept the performance compromise involved, let alone the expense and the faff of additional coupling adapters - probably explains why the 1 inch bsp version sells at just over a hundred quid *plus VAT*).
Anyhow, the point of this particular exercise was to closely examine every last repair option at my leisure (in summer time, the 3KW immersion element serves our hot water needs quite nicely, thank you very much!), before being forced to shell out for a brand new zone valve assembly.
I was able to determine that the 5rpm synchromotor unit still functioned despite the expected stiffness of the integral 100:1 reduction gearbox (the motor appears to be a 12 pole affair, 500rpm at 50Hz). There was no hint of gearbox damage as exemplified in some of the many (often misleading) Youtube videos on the subject of repair/replacement of the V4073A 3 port (2 way) zone valve that I had the displeasure to watch.
If there *is* a decent DIY wiki on the subject of dealing with this zone valve and all of its many variants, I'm afraid my googling failed to reveal it. Feel free to point me to one if such exists.
I'm not a heating engineer by trade, just an engineer with an interest in how a wide range of stuff *actually* works, from basic first principles to the nitty gritty of real world implementations.
It's quite apparent that most of the Youtube videos on this subject were produced by well meaning amateurs who had less than a full understanding of the mechanism (but enough not to place their followers at undue risk and to offer, if not entirely optimal, repair options).
For instance, one chap didn't realise that the synchromotor unit only ran one way regardless of the polarity of its connection so advised unnecessary care in duplicating the polarity of the connections - not of any detriment at the end of the day, just a needless concern in the mind of his audience. Sadly, most of these 'instructive' videos were laced with similar nuggets of misinformation.
One such 'nugget' was to imply that removing all four motor head retaining screws (on the older type of control valve) would result in a disastrous flood of water with no indication that when faced with such, you merely had to drain the system down *beforehand* just as you'd need to in order to replace the whole valve assembly with a new one in order to effect the repair. IOW, once you've drained the system down, you *can* safely remove the motorhead from the old style unit if you wish to avoid unnecessary disturbance to the plumbing (assuming you have sufficient access to make this a realistic option).
Getting back to my particular situation, once I'd uncoupled the synchromotor (2 screw fixing), I could see that there was no undue binding in the mechanism nor in the valve bearing. I could turn the output cog on the motor's integral gearbox by finger, just! The stiffness seemed more a case of fighting the resistance of heavy duty grease in a 100:1 ratio gearbox rather than mechanical binding from worn gearbox bearings. However, without the example of a brand new motor/gearbox assembly by which to judge the old one, it's hard to say whether such resistance is unduly higher than it's supposed to be. One of the youtube videos offered a hint that excess resistance could be a major contribution to my problem.
With the old motor unit reinstated, I was able to exercise the unit through a range of movement well beyond the limits imposed by the rubber ball contacting the valve seats when completely reassembled.
One oddity I noticed was that I was only able to get the mechanism to return completely to the limit stop under spring tension alone in every other orientation *except* the one it had to operate in. Even so, this restricted return range still comfortably exceeded that imposed by the ball landing on the A port valve seat, even when the motor (with its end cap removed) was wound in the reverse direction to effect a tight enough seal to block my attempts at blowing air into the A port.
Releasing the motor's rotor allowed the pressure generated by deforming the rubber ball into forming an airtight seal into causing the motor to run forwards again against all the spring tension and the resistance of the gearbox.
The surface of the rubber ball is still a little rough despite my best attempts at scrubbing the deposits off with a miniature brass wire brush. It's also a little bit dented and slightly deformed, all of which suggests that a new one will go a long way, if not all the way, to effecting a cure. I suspect that a new synchromotor wouldn't come amiss either (but only if I can replace the rubber ball - it wouldn't really be worth doing this on its own).
Rather than wait for replacement parts, I decided to refit the valve to test whether any of my 'fettling' has effected any sort of improvement. It occurred to me, going by the warnings in regard of the fitting of the valve to be restricted to the A-B port only being connected to the output port of the CH pump that quite possibly, the water flow /pressure differential will have a servo effect on the closing of each port as the perfect and unblemished rubber ball is brought into precisely aligned contact with either valve seat (not so critical for the motor assisted landing on the B port but a great boon to closing off the return spring driven contact with the A valve seat).
Obviously a thesis that requires the valve assembly to be reinstated into the plumbing in order to make the necessary tests to prove or disprove the theory. The only conclusion I was able to come to was that "I hadn't made it any worse" :-(
Looking on the bright side, after a modest bit of cleaning up of the pipe ends around the compression joint olives, I was able to easily reinstate the valve without any signs of leakage, not just at the pipe joints but also from the O ring seal between the valve body and the motorhead base plate in spite of re-using the original O ring.
I notice that there is a rubber ball refurbishment kit available for the later version valve. If the rubber ball part is identical to the one used by the earlier valve, I'll be able to cannibalise it from that repair kit if it proves impossible to buy just the ball part on its own.
I've yet to delve into this possibility but if I *can* replace the ball, I figure a new motor *would* then make a worthwhile add on to my refurbishment parts list. If I can't replace the rubber ball, there seems very little point in replacing the motor on its own and I'll be 'biting the bullet' and lashing out on a 'proper' V4073A6022 with 1 inch BSP fittings for something like 120 odd quid.
If anyone cares to offer the benefit of their experience in regard to my Central Heating repair saga, please feel free to add whatever comments and advice you may see fit to offer. I *think* I've covered all the angles but I'm quite amenable to considered suggestions from others more experienced in these matters.
Johnny B Good
Johnny B Good