Doing a diverter on a CB28 tomorrow and being a Saturday I want to be in and out pretty sharpish. I usually drain the top floor rads, but can the valves be trusted not to leak? Last thing I want at the weekend is to put the boiler out of action. Boiler is about six years old. Are the valves any good or guaranteed leakers (like Worcesters).
Alpha CB Isolating valves
- Thread starter avidfan
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There is a proper drain point underneath think I used to use a 12mm box spanner for ease, might not be 12mm but something like, my memory is shot to bits.
I never had a problem using the isolating points on that generation of Alpha the didn't leak afterwards.
It's a very clumbsy diverter valve plate heat exchanger design. Quite a wrestling match, I think it's the big horizontal nut on the left which I used to use my grips backwards to get on it. I don't recall now the way to make it go smoothly in reassemby, it might be that particular nut has to be started first it might be another. Put it this way if you do the nasty one last you are in trouble. Just catch a thread or two on all of them. The fit is very bad the pipes get distorted into place as you tighten up.
The primary flow and return pipes often need new red o rings at the top where they enter the primary heat exchanger. Do this at the same time.
If it's only the diaphragm which it invariably is (after proving it isn't the flow switch , which is the much more common failure) just remove the pump and take only the dhw housing off change diaphragm, return it. Much easier job much less disruption.
Oh I nearly forgot the most significant problem part of the job. There is a no 0 or 1 (small anyway) philips head grubscrew holding the diverter valve securely to the cold water supply. If this were not secure the cold pressure would blow it clean off it's o ring seal. There are two stages of this a male part with o ring seal held on by a tiny grubscrew fits into a M/F brass manifold of same construction seal and retention method which in turn interfaces with the iso valve manifold. If one of these won't undo you can undo the other to remove valve and then deal with the probem on the bench.
One way to deal with the problem of the mechanical head of this screw bbeing insufficiently contructed to power it into an undone position, is to use a hacksaw blade and make a slot screw out of it. Only do this if your phiulips driver chews it. When that fails, which invariably it does, try removing the other part with it. If that fails drill it out and buy a new manifold. Some people tap in a new screw but if you do that and it fails you flood the house. New part is recommended method. This nasty part of the job is all avoided if you have plenty of skill use the highest quality screwdrivers of exact right fit and push with the power of an elephant while turning with the power of a flea. Sadly most people can't adopt the intelligent approach and have already wrecked the delicate philips head, following wich the above chain reaction ensues. Haven't found a trainee yet who naturally knows how to undo a screw.
I never had a problem using the isolating points on that generation of Alpha the didn't leak afterwards.
It's a very clumbsy diverter valve plate heat exchanger design. Quite a wrestling match, I think it's the big horizontal nut on the left which I used to use my grips backwards to get on it. I don't recall now the way to make it go smoothly in reassemby, it might be that particular nut has to be started first it might be another. Put it this way if you do the nasty one last you are in trouble. Just catch a thread or two on all of them. The fit is very bad the pipes get distorted into place as you tighten up.
The primary flow and return pipes often need new red o rings at the top where they enter the primary heat exchanger. Do this at the same time.
If it's only the diaphragm which it invariably is (after proving it isn't the flow switch , which is the much more common failure) just remove the pump and take only the dhw housing off change diaphragm, return it. Much easier job much less disruption.
Oh I nearly forgot the most significant problem part of the job. There is a no 0 or 1 (small anyway) philips head grubscrew holding the diverter valve securely to the cold water supply. If this were not secure the cold pressure would blow it clean off it's o ring seal. There are two stages of this a male part with o ring seal held on by a tiny grubscrew fits into a M/F brass manifold of same construction seal and retention method which in turn interfaces with the iso valve manifold. If one of these won't undo you can undo the other to remove valve and then deal with the probem on the bench.
One way to deal with the problem of the mechanical head of this screw bbeing insufficiently contructed to power it into an undone position, is to use a hacksaw blade and make a slot screw out of it. Only do this if your phiulips driver chews it. When that fails, which invariably it does, try removing the other part with it. If that fails drill it out and buy a new manifold. Some people tap in a new screw but if you do that and it fails you flood the house. New part is recommended method. This nasty part of the job is all avoided if you have plenty of skill use the highest quality screwdrivers of exact right fit and push with the power of an elephant while turning with the power of a flea. Sadly most people can't adopt the intelligent approach and have already wrecked the delicate philips head, following wich the above chain reaction ensues. Haven't found a trainee yet who naturally knows how to undo a screw.
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Cheers gents. Quite agree Paul I always take great care with that screw. Alpha service guy warned me about it a couple of years ago. I usually stick the pozi driver in it then give it a sharp tap. Haven't had one shear yet. If you buy the large seal/washer kit you get a couple of spare screws in it, but not with the smaller kit. On the subject of the pipes not aligning, you must be carefull when tightening up and pulling them together. One I did a couple of months ago ended up with me wrecking the plate exchanger. Brass connector started leaking where it's made on to the s/steel plate. Thought I could unscrew it and remake the joint. Big mistake, male thread distorted due to waffer thin construction. Won't try that again.
I couldn't agree more.
Replacing a prv if it doesnt re-seat is a fraction of the cost of replacing the isolating valves.
But the point is there is a drain off on the boiler why replace a prv when not required?
And I have never had an Alpha CB iso valve leak and I had them on the van with me at no cost to myself so had any leaked I would have changed them.
Don't tar all manufacturers with the same brush the clearly use differenmt sources for isolation valves. Some use a source which you must never operate the valves after install.
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im desperately trying to remember where the drain off is on a CB.
if you have never had a CB iso leak then count yourself lucky paul. i keep them in that van not because i use them but because i regard them as unreliable. i accept this could be due to the water in my area though.
Drain off is about 1/3rd from right almost halfway back, can just about get grips on it with front panel folded down but very easy with a box spanner, which also ducts the water to your bucket.
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