Thermostaticaly controlled mixer shower + angry wife!

[chrishutt]

... trapped air that was contributing to cavitation in the pump.

Does trapped air contribute to cavitation? What evidence was there of cavitation in the central heating pump?

It's all very well cutting and pasting from internet sites (though you really should identify your sources) but if you don't really understand the subject you'll end up looking a bit silly.

 

[Last Triumph]

... trapped air that was contributing to cavitation in the pump.

Does trapped air contribute to cavitation? What evidence was there of cavitation in the central heating pump?

It's all very well cutting and pasting from internet sites (though you really should identify your sources) but if you don't really understand the subject you'll end up looking a bit silly.

Haven't cut n'pasted anything, just remembering back to college. And yes, to be honest, cavitation is very difficult to positively identify within a central heating system, especially if there is air already trapped in there.

However, if air was trapped, and this was to cause a recuction of flow, yet the pump was still to turn at high speed with reduced water pressure, it is entrirely possible for cavitation to occur, but yeah, to be fair this is unlikely.

I'm not a fluid dynamacist, and as you can tell I'm certainly not a central heating engineer, hence I've come on here for help and advice from you good people who have more knowledge and experience than me.

 

[chrishutt]

Haven't cut n'pasted anything, just remembering back to college.

Sorry, I shouldn't have suggested that. And you're right that trapped air might add to flow resistance and so provoke cavitation. However cavitation is more likely to occur with shower pumps than domestic heating pumps since shower pumps are generally rated at 1 bar and above.

 

[Last Triumph]

No worries - at least the heating side of things is sorted now - except for the jungle-gym of copper pipe!

I'll call the Hudson Reed help line tommorrow and describe the problem - I just hope they can come up with an answer that doesn't involve removing the valve - that would be hideous!

 

[chrishutt]

With regard to the shower, are you sure that the shower valve and pump have been installed in accordance with the instructions for both? For example most shower pumps require that the hot supply is taken from the cylinder via a special "flange" or boss which is designed to avoid entraining air (which is normally given off by the cylinder water as it is heated).

What about the adjustment of the temperature setting on the shower valve? From your description it sounds as if you might be coming to the limit of adjustment before the desired temperature is reached. This can easily be adjusted.

 

[ChrisR]

You won't get cavitation in a domestic heating system, especially with the pump on setting 2.

You shouldn't get air trapped either. There may be a partial blockage. Try a magnet against the pipes at the top right of
picture 1,
where the feed pipe joins, especially.

For your shower, make sure its hot supply gate valve is full open (less half a turn!), and try progressively closing the cold supply valve. It won't hurt the pump to run with a dead end for a quick test.

You should find you can take the shower valve apart from the front. Bits of dirt can easily stick in there, or the catridge may need changing.

SUpplying the hw side of the pump from somewhere on the pipes is ok IF the supply to the hw cylinder is low resistance. It often turns out that 22mm is too small, so it's easier for the pump to suck air down the vent pipe.

 

[Last Triumph]

You won't get cavitation in a domestic heating system, especially with the pump on setting 2.

You shouldn't get air trapped either. There may be a partial blockage. Try a magnet against the pipes at the top right of
picture 1,
where the feed pipe joins, especially.

For your shower, make sure its hot supply gate valve is full open (less half a turn!), and try progressively closing the cold supply valve. It won't hurt the pump to run with a dead end for a quick test.

You should find you can take the shower valve apart from the front. Bits of dirt can easily stick in there, or the catridge may need changing.

SUpplying the hw side of the pump from somewhere on the pipes is ok IF the supply to the hw cylinder is low resistance. It often turns out that 22mm is too small, so it's easier for the pump to suck air down the vent pipe.

The central heating and hot water is working fine now and is fairly quiet, except for the leaking honeywell valve.

Just out of interest - what does the magnet technique do?

All gate valves and pipe runs check, open and correct.

Cold water is taken from the header tank using a 22 mm essex flange.
The instructions for the valve / pump said a T-Piece supply for the hot is okay as long as it is sited a long enough distance away from the vertical vent joint. I'm over a foot below this line.

I've tried closing the cold off without the pump running and yes it gets hot that way which tells me that there is a problem with the valve.

Just come off the phone to Hudson Reed who said, "Ah yes, it's proabaly another case of a stuck 'o' ring preventing the valve opening enough on the hot side, I'll send you a new 'o' ring pack......"

Well, good news that I might have found a solution.

Bad news that I spend over £300 on what is meant to be top quality gear to find they have a known fault.

Worse news that I'll probably have to remove the cover plate and dig out the tiles around the valve.

And no, I didn't leave space to work on it - tiled and grouted right up to the valve body - I mean what could go wrong - it's top quality gear with a 10 year guarentee...

 

[ChrisR]

The instructions for the valve / pump said a T-Piece supply for the hot is okay as long as it is sited a long enough distance away from the vertical vent joint.

Then they're wrong, for the reason I explained. It could also be too far!

"Ah yes, it's proabaly another case of a stuck 'o' ring preventing the valve opening enough on the hot side, I'll send you a new 'o' ring pack......"

Not good enough. Tell them to send their engineer to fix it, or you'll send them the bill.

Most HR mixers like these can be accessed from the front .

 

[Last Triumph]

The instructions for the valve / pump said a T-Piece supply for the hot is okay as long as it is sited a long enough distance away from the vertical vent joint.

Then they're wrong, for the reason I explained. It could also be too far!

"Ah yes, it's proabaly another case of a stuck 'o' ring preventing the valve opening enough on the hot side, I'll send you a new 'o' ring pack......"

Not good enough. Tell them to send their engineer to fix it, or you'll send them the bill.

Most HR mixers like these can be accessed from the front .

Thanks Chris.

I'll wait for the parts to turn up and see what's involved. If it looks like a real ball acher, I might give them a call and see what they can do to help.

I asked if it could be accessed from the front and all she said was that I'll need to remove the large cover plate to gain access to the valve body....

Well, I can't see how this will help, as other than the water inlet / outlets, there is no other access than the front. Which if this is the case, taking the cover plate off isn't needed. Like I say, I'll see what turns up and look at the instructions that they said they'd send with the parts.

The pic of that valve you linked to is similar to mine, so it'll be great if it can be done from the front like you say. This is the exact model I have...

http://www.heatandplumb.com/acatalog/main_product_HRA3193.jpg

I take on board your comments about the T-Piece location. I've tried the shower without the pump and whilst flow is reduced, the symptoms are the same, even on a reduced flow on the shower valve itself.

Don't suppose you've got a pic, or link to a pic of what, where and how the ideal hot water take off should be sited on an installation similar to mine?

It doesn't spit or surge at all like I'd expect if it was drawing air, but I couldn't be certain. Then again, I get hot through in a constant flow when the cold is totally shut off so hopefully air isn't the problem.

Fingers crossed the valve o ring issue is the cause and easy to rectify.

Thanks once again for all your input.

 

[Last Triumph]

Just out of interest, here is the PDF instructions that came with my shower pump.

http://www.newteamshowers.com/proje...ces/404-0131_0504.PDF/$File/404-0131_0504.PDF

Page 6 mentions the T piece hot water connector. I admit that it also suggests an Essex flange to the hot water cylinder, but only if the T-piece is not possible.

At leaet I know I wasn't imagining things...

 

[Balenza]

Last Triumph wrote

Don't suppose you've got a pic, or link to a pic of what, where and how the ideal hot water take off should be sited on an installation similar to mine?

try here...
http://www.stuart-turner.co.uk/PDF/17559-30-11.pdf

or here...
http://www.salamanderpumps.co.uk/Download/instructions.pdf

 

[Last Triumph]

Last Triumph wrote

Don't suppose you've got a pic, or link to a pic of what, where and how the ideal hot water take off should be sited on an installation similar to mine?

try here...
http://www.stuart-turner.co.uk/PDF/17559-30-11.pdf

or here...
http://www.salamanderpumps.co.uk/Download/instructions.pdf[/QUOTE]

Thanks.

It would appear, that whilst not the ideal solution, the T adaptor is accepted as an option, and that my set up falls within specs for this type.
I take it this is all in an effort to stop it drawing air? Or are there other problems with this set up?

 

[Balenza]

Last Tuesday wrote

It would appear, that whilst not the ideal solution, the T adaptor is accepted as an option, and that my set up falls within specs for this type.

What you have installed is the least preferred method.

I take it this is all in an effort to stop it drawing air?

Yep. And to prevent other flow influences affecting the suction side of the pump.

Or are there other problems with this set up?

Someone turning on a hot tap somewhere else in the premises whilst the pump is in operation may increase the chances of air being drawn down the vent pipe.

 

[Last Triumph]

Cheers.

On the basis that the problem at the shower end stays the same even with the pump switched off and the flow reduced to very little, and there has never been any surging or pulsing in flow or variance in temperature once set, I guess I can assume that I'm not drawing air?

Or am I mistaken AGAIN?

 

[ChrisR]

Air-sucking is unpredictable. It certainly wouldn't do it with the pump off though. it quite often only starts after a few minutes or if another tap's turned on. It makes a racket in the pump so you'll soon know. Don't ignore strange noises though, it can damage pumps.