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Author Topic: Wetback Problem  (Read 8478 times)

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Offline Murray Glue

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Wetback Problem
« on: May 17, 2013, 10:47:15 AM »
I have had a 3Kw manufacturers original wetback installed in a Metro wood stove ( the small model ). Previously it had a booster wetback installed which included a pulse valve, but we got sick of the banging and crashing that went on when the fire was lit. Now, I get no thermosiphon with the new one at all, and no hot water in the cylinder...or so it appears. After a short period of running the fire I get hot water in both the up and down piping from the wetback ( the cylinder is in the roof about 3 metres above the stove, so you would expect thermo siphoning to not be a problem ).

The cylincer is small ( about 135 litres )...and it has a tempering valve installed. Is it possible that the temering valves is causing hot water to flow down to the wetback, or is it simply that both connections to the wetback are rising??  Are tempering valves adjustable?

I have called the plumber back but I would love to know whats going on myself before he gets round to coming> Appreciater any thoughts!!!

Murray



Linkback: https://www.plumbers.nz/q-and-a-wetbacks/61/wetback-problem/1463/

Offline Plumber

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Re: Wetback Problem
« Reply #1 on: May 17, 2013, 12:44:07 PM »
Hi Murray, a few questions please

  • Do you know what pipe size was run from the HWC to the wetback 20mm? or 25mm?
  • Can you post a diagram of where the tempering valve was installed? It should not be on the wetback side at all
  • Is the wetback open vented and where is the cold (live) water pipe connected, on the flow or return?
Please note that the advice I am giving is only my opinion and not necessarily a fact.  Please refer to our terms and conditions.

Offline Murray Glue

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Re: Wetback Problem
« Reply #2 on: May 22, 2013, 01:33:11 PM »
Hi and thanks for your reply. Sorry its taken me a while to get back to you...

The piping from the cylinder down to the wetback is the same as was installed for the 3Kw " Pulse Valve " model I took out. Its 20mm but it is smaller than the tubing ends that stick out of the new 3kw wetback, which are 25mm.

The plumber had to do some squashing ( not a professional plumbing term, but thats what he did ), to get it to where he could weld one to the other. Could this reduction in pipe sizes be the cause of the problem?

I crawled into the roof space to check: the tempering valve is connected between the top of cylinder outlet ( H ) and the cold water supply ( C ) and outputs to the hot water taps in the house. I guess this is to cool the water if it gets too hot at the top of the cylinder. So, no its not in the wetback side of things. My apologies for throwing that one in.

Yes the wetback up-pipe goes to the top of the cylinder where it is open vented through a standpipe on the roof, which is lagged and sleeved, and is about 3 m high. The cold water down to the wetback comes directly out of the cylinder a few inches above the base of the cylinder, which is my experience of where it should come from.

The wierd thing is that when you light the fire from cold, you get  gradual heating of the riser side, while the down pipe stays cold, or cool anyway...then after fifteen or twenty minutes there is usually a succession of gurgles and burps, and some rattling of the whole set-up, after which it settles down but both pipes appear to be rising. Eventually there is very little difference between the riser and the down-pipe as far as temperature are concerned, but there is little or no boosting of the water in the cylinder when you go to take a shower.

I would love to get this sorted out....so any input would be gladly received. I have installed a couple of systems before, myself, and they have worked fine. One included a temperature controlled pump to do the circulating as there was a distance of several metres horizontally and with no rise to the cylinder. But this one is a straightforward setup and should work without issues.

Is it possible that I should instal a non return in the downpipe...to replace the pulse valve that was in the existing system before I decided to change the wetback?  ( And wish I hadnt!! )...I was told that its bad plumbing practice to instal any kind of restricting valve in a wetback system, in case it fails.

Cheers

Murray





Offline Murray Glue

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Re: Wetback Problem
« Reply #3 on: May 23, 2013, 09:05:22 AM »
Hi again,

I have made up a diagram of how the house is plumbed.  Note that the solar panel works very well in summer to boost the HWC temperatures and we often turn off the water heating on sunny days. The fire was lit last night for 6 hours with the usual results. Can you see anything wrong with this setup ( done by previous owners )?

Offline Plumber

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Re: Wetback Problem
« Reply #4 on: May 23, 2013, 09:42:27 AM »
Very good diagram :) , The tempering valve is not the problem what confuses me straight away is that your flow is running into your open vent above the body of water in the tank (should be about 300mm above the return, as the hot water has no more space to rise it cant contribute to the circulation) This explains why they used a pulse valve. Also part of the problem is that your solar is on the same circuit this is bound to disrupt the natural circulation.

The greater the vertical height of a circulation system , the greater will be the circulating pressure. The greater the difference in temperature between the "hotter" rising flow and the "cooler" falling return, the greater the circulation pressure. Also the simpler and shorter the circulation system the smaller the loss of circulating pressure due to friction.  The amount of bends you have are too many and not swept enough and having a 20mm pipe does not help the cause at all. Sorry but looking at this I think without reconfiguring the system thermal circulation is impossible. If you don't llike the noise of the pulse valve I would suggest a thermostat triggering a pump, I know it defeats the purpose of a wetback using an electrical solution also this needs to be installed correctly as it can push water through the vent if not done properly. If it was my place I would redo the wetback or put up with the pulse valve. Hope this helps some what..  :-\

Offline Murray Glue

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Re: Wetback Problem
« Reply #5 on: May 23, 2013, 11:45:21 AM »
 ;D

Hi,

Thanks very much for looking at the diagram and responding. A picture is worth 1000 words in this case. Yes I agree with what you say, and its obvious to me now that the pulse valve was there for a good reason. I wish it had been obvious to the plumber who did the replacement work for me.  I have done some research into the available pulse valves on the market, and came up with a phone number that I have since called and spoken to a guy who is making the valves near where I live in Kerikeri.  He has some first hand experience with the original installer of the system, and what he says ties in with your thoughts.

I am going to invest in one and get it installed. I will get back on the site and report on the outcome!

Murray

Offline robbo

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Re: Wetback Problem
« Reply #6 on: May 23, 2013, 12:59:18 PM »
hi guys/Murray/Plumber, just to add my two cents worth, your diagram pipework looks like the wetback would be heating the solar panel and by-passing the h/w cylinder which by the way looks far,far too small to need a wetback and solar system to heat, if it worked correctly it would quickly relieve water out of the exhaust and continuously also why do you need two vents? what do you think Plumber? cheers

Offline Plumber

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Re: Wetback Problem
« Reply #7 on: May 23, 2013, 07:45:26 PM »
Yes Robbo that T does look odd but it looks like both the solar and wetback are drawing the cold water from that point. Would need a better understanding of the actual solar system but assume there is a pump and non-return somewhere allowing for separation requiring two vents to keep both systems flooded.. But I'm just guessing :) Your right about the size of the tank way to small for a wetback and solar.  :o Look forward to your update Murray!

Offline integrated

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Re: Wetback Problem
« Reply #8 on: May 23, 2013, 07:58:15 PM »
I think all you really need is an anti-siphon loop in the return pipe down by the boiler - return pipe only

the cooler more dense & heavier water volume in the loop would force the heated water up and through the flow pipe towards the hwc creating the ciculation you require

obviously not as pretty as std pipework or perhaps a pulse valve - but wont be as noisey either

what is the design of the wetback like? are the ports over/under as drawn or are they in fact side by side?

Offline Murray Glue

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Re: Wetback Problem
« Reply #9 on: May 24, 2013, 09:31:19 AM »
Hi,

the solar panel is a standard old fashioned copper matrix with a top and bottom manifold tube of about 25mm and 10 or so smaller vertical tubes. There is a unit fitted to the top connection which I assume is a non return valve to stop water flowing back into the panel....it all works really well and makes alot of difference to the water temperature. I think the two open vents are there so that there is a header pressure for the 2 systems and so that the pump isnt always switching on.

The outlets on the wetback are indeed over and under and about 6 inches apart, vertically.

Can you sketch and anti siphon loop? Is this like you use on marine toilets to stop them back siphoning and sinking your boat?

Cheers all

Murray

Offline Murray Glue

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Re: Wetback Problem
« Reply #10 on: June 05, 2013, 03:07:37 PM »
Hi,

Happily to relate that the insertion of a NZ made Pulse Flow Monitoring valve has cured the problem; no more banging and crashing, just a steady almost silent circulation and lots of hot water!! We left the circulating pipework at 20mm and the hotwater riser still goes to the top of the cylinder. Thanks to those who contributed, especially Plumber.
Just goes to show that sites like this one can be very useful in cutting through alot of the bull**** and getting to the core of the problem.

Murray

Offline Plumber

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Re: Wetback Problem
« Reply #11 on: June 06, 2013, 08:13:44 AM »
Cheers for the update Murray, I would be interested in the brand of that pulse valve please.

Offline Murray Glue

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Re: Wetback Problem
« Reply #12 on: June 06, 2013, 08:46:37 AM »
Hi

Sure, no problem. They are made in a brass housing by a small industry in Kaeo, New Zealand. The contact is Merv Foley, Mobile: 021 882542 or A/H 09 4050591. Email pulse.flow@xtra.co.nz. He has a website at www.pulseflow.co.nz.

They have a 5 year warranty, well constructed, and come with details on proper installation.

Cheers

Murray

Offline Plumber

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Re: Wetback Problem
« Reply #13 on: June 07, 2013, 09:42:46 AM »
Cheers for that Murray, will certainly give them a bell  :)


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