Megaflow problem


Model CL250. Over pressure valve on cold water inlet bleeds warm water. New pressure/temp valve fitted. New combination valve assembly fitted. Over pressure valve on water inlet still bleeds. Regulator factory set to 3 bar. Over pressure valve factory set to trigger at 8. What possible problems or faults match these symptoms?
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Failed air bubble - read the replenishment instructions
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Janet Bale wrote:

i.e., expansion relief valve dripping; refill air bubble as stated above. The expansion bubble/expansion tank isn't required in most other countries, where the expansion relief valve just dumps the extra water volume down the drain. The expansion tank or bubble is a UK Water Bylaws requirement to prevent waste of water.

Why? They would have had to drain the heater, and so refill the air bubble, to fit a new T&P relief valve. The T&P valves rarely fail.

Why?
I've been told that you can get a recurring loss of the air bubble in some areas, due to the water quality. In this case the fix is to fit an external expansion tank, or refill the air bubble regularly. Ring the manufacturers for technical advice. Anyone doing work on an unvented water heater should have passed the relevant training course (IoP, CITB, etc., ). If you're going to ask for a refund for any unnecessary work from the installer, ask for the relevant certificate number and check with the issuing body.
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If all else fails, you could always resort to reading the manual which should have come with the heater or, if not, it is available on the Heatrae Sadia website.
The manual says;
Water discharges from Expansion Relief Valve 1. INTERMITTENTLY Expansion volume has reduced within unit. See Section 7.4 for recharging procedure
2. CONTINUALLY a.    Cold Water Combination Valve Pressure Reducer not working correctly. Check pressure from Cold Water Combination Valve. If greater than 3 bar replace Pressure Reducer cartridge b.    Expansion Valve seat damaged. Remove Expansion Valve cartridge. Check condition of seat. If necessary fit new Expansion Valve cartridge.
I couldn't have put it better myself.;-)
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Thanks to all that responded. However all of your useful and valid suggestions have been tried. Heatrae technical help have offered an explanation for the bubble loss and suggested a fix. If they are correct I can also see another way to remove the problem. If either are successful I will report in full for the benefit other others.
Thanks,
Martin
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Janet Bale wrote:

Could you tell us what that is, please? Thanks
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This is a multi-part message in MIME format. --------------000300030607000104050201 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
Aidan wrote:

The Megaflo feeds the hot water system in a holiday rental barn conversion. The cold water is all at mains pressure, hence the system is not balanced. There are three shower mixers and other mixer taps. Heatrae suggested that one or more mixers were bleeding cold water across to the hot water system thus raising the pressure in the Megaflo to the point where the inlet valve blows at 8 bar and a reverse flow occurs with hot water pouring down the tundish. Their solution was to fit a double check valve on the hot water outlet of the Megflo. This cured the problem completely. I also fitted a pressure gauge on the cold inlet so that this can be monitored. Obviously a proper solution would be to connect the cold system to the cold tee off on the regulator. This would stop the hot water system being raised in pressure. However the tight space and complexity of pipe work makes this at least half a days work plus materials. Now that all is apparently well, the customer is taking some convincing that they should go for this.
Martin
--------------000300030607000104050201 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> <br> Aidan wrote: <blockquote cite=" snipped-for-privacy@g14g2000cwa.googlegroups.com" type="cite"> <pre wrap="">Janet Bale wrote: </pre> <blockquote type="cite"> <pre wrap=""> Heatrae technical help have offered an explanation for the bubble loss and suggested a fix. </pre> </blockquote> <pre wrap=""><!----> Could you tell us what that is, please? Thanks </pre> </blockquote> The Megaflo feeds the hot water system in a holiday rental barn conversion. The cold water is all at mains pressure, hence the system is not balanced. There are three shower mixers and other mixer taps. Heatrae suggested that one or more mixers were bleeding cold water across to the hot water system thus raising the pressure in the Megaflo to the point where the inlet valve blows at 8 bar and a reverse flow occurs with hot water pouring down the tundish. Their solution was to fit a double check valve on the hot water outlet of the Megflo. This cured the problem completely. I also fitted a pressure gauge on the cold inlet so that this can be monitored. Obviously a proper solution would be to connect the cold system to the cold tee off on the regulator. This would stop the hot water system being raised in pressure. However the tight space and complexity of pipe work makes this at least half a days work plus materials. Now that all is apparently well, the customer is taking some convincing that they should go for this.<br> <br> Martin<br> </body> </html>
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Janet Bale wrote:

Thanks; I've not heard of that happening.
It's a common installation problem where the Megaflo is some distance from where the CWM enters the building.
Another option might be to fit a strainer & a pressure reducing valve on the cold water mains supply, to reduce the cold pressure to the 3.5 (?) bar the Megaflo operates at. Presumably the CWM is more accessible, since you've been able to put a pressure gauge on it. The disadvantage is that you've got 2 sets of pressure reducing valves where one might have done & the Megaflo pressure reducing valve is only getting a 3.5 bar supply, unless you can put in a dedicated supply pipe..
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Aidan wrote:
Same problem discussed (& resolved) here; http://www.screwfix.com/talk/thread.jspa?threadID $253&messageID#7453#237453
NB the mention of the occasional loss of pressure.
The manufacturer's explanation doesn't quite make sense; if that was happening, you'd get a cold shower & the expansion relief valve (6 bar ?) would operate before the T&P relief valve (8 bar?). You should notice the water being discharged.

Ignore that; if you could do that, then you'd be able to connect the cold supply to the tee after the Megaflo multi-function valve.
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This is a multi-part message in MIME format. --------------080108030803040104030207 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
Aidan wrote:

Thanks for the screwfix pointer. That gave me the clue that some or all of the shower mixers may be fed with a higher pressure on the cold side than they are designed for. Hence the bleed through to the hot side. This would not necessarily give a cold shower as the flow rate would be very low.
I don't know if the CL210 is different to the CL250 but the expansion relief valve is 8 bar whilst the T/P valve is 90C/10 bar. This is why the T/P valve does not go first. I can now say to the customer that if her shower mixers are not rated that high then she should have the cold side corrected. Or maybe even if the mixers were rated at over 10 bar for a balanced supply, they would not stand that amount of imbalance?

Yes, tight space with several cold tee offs close together make this difficult.
--------------080108030803040104030207 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> <title></title> </head> <body bgcolor="#ffffff" text="#000000"> <br> <br> Aidan wrote:<br> <blockquote cite=" snipped-for-privacy@j33g2000cwa.googlegroups.com" type="cite"> <pre wrap="">Aidan wrote:
Same problem discussed (&amp; resolved) here; <a class="moz-txt-link-freetext" href="http://www.screwfix.com/talk/thread.jspa?threadID $253&messageID#7453#237453">http://www.screwfix.com/talk/thread.jspa?threadID $253&amp;messageID#7453#237453</a>
NB the mention of the occasional loss of pressure.
The manufacturer's explanation doesn't quite make sense; if that was happening, you'd get a cold shower &amp; the expansion relief valve (6 bar ?) would operate before the T&amp;P relief valve (8 bar?). You should notice the water being discharged. </pre> </blockquote> Thanks for the screwfix pointer. That gave me the clue that some or all of the shower mixers may be fed with a higher pressure on the cold side than they are designed for. Hence the bleed through to the hot side. This would not necessarily give a cold shower as the flow rate would be very low.<br> <br> I don't know if the CL210 is different to the CL250 but the expansion relief valve is 8 bar whilst the T/P valve is 90C/10 bar. This is why the T/P valve does not go first. I can now say to the customer that if her shower mixers are not rated that high then she should have the cold side corrected. Or maybe even if the mixers were rated at over 10 bar for a balanced supply, they would not stand that amount of imbalance?<br> <blockquote cite=" snipped-for-privacy@j33g2000cwa.googlegroups.com" type="cite"> <pre wrap=""> </pre> <blockquote type="cite"> <pre wrap="">bar supply, unless you can put in a dedicated supply pipe. </pre> </blockquote> <pre wrap=""><!---->Ignore that; if you could do that, then you'd be able to connect the cold supply to the tee after the Megaflo multi-function valve. </pre> </blockquote> Yes, tight space with several cold tee offs close together make this difficult.<br> </body> </html>
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Aidan wrote:
Aidan wrote:
Same problem discussed (& resolved) here; http://www.screwfix.com/talk/thread.jspa?threadID $253&messageID#7453#237453
NB the mention of the occasional loss of pressure.
The manufacturer's explanation doesn't quite make sense; if that was happening, you'd get a cold shower & the expansion relief valve (6 bar ?) would operate before the T&P relief valve (8 bar?). You should notice the water being discharged.
Thanks for the screwfix pointer. That gave me the clue that some or all of the shower mixers may be fed with a higher pressure on the cold side than they are designed for. Hence the bleed through to the hot side. This would not necessarily give a cold shower as the flow rate would be very low.
I don't know if the CL210 is different to the CL250 but the expansion relief valve is 8 bar whilst the T/P valve is 90C/10 bar. This is why the T/P valve does not go first. I can now say to the customer that if her shower mixers are not rated that high then she should have the cold side corrected. Or maybe even if the mixers were rated at over 10 bar for a balanced supply, they would not stand that amount of imbalance?

Ignore that; if you could do that, then you'd be able to connect the cold supply to the tee after the Megaflow multi-function valve.
Yes, tight space with several cold tee offs close together make this difficult.
Doesn't the Megaflow have a pressure equalising valve on the cold inlet to the Megaflow? All cold is supposed to be taken from this valve at the cylinder. It equalises the hot and cold but does not take into account pressure loss through the megaflow, which appears to be the problem here, so an imbalance of hot and cold pressure at the appliances. Mixers with pressure equalisation valves can do the trick, or a 22mm pressure equalisation valve on the megaflow outlet and all appliances have their cold taken from this, then the pressure drop across the Megaflow is taken into account.
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The Megaflo feeds the hot water system in a holiday rental barn conversion. The cold water is all at mains pressure, hence the system is not balanced. There are three shower mixers and other mixer taps. Heatrae suggested that one or more mixers were bleeding cold water across to the hot water system thus raising the pressure in the Megaflo to the point where the inlet valve blows at 8 bar and a reverse flow occurs with hot water pouring down the tundish. Their solution was to fit a double check valve on the hot water outlet of the Megflo. This cured the problem completely. I also fitted a pressure gauge on the cold inlet so that this can be monitored. Obviously a proper solution would be to connect the cold system to the cold tee off on the regulator. This would stop the hot water system being raised in pressure. However the tight space and complexity of pipe work makes this at least half a days work plus materials. Now that all is apparently well, the customer is taking some convincing that they should go for this. <<<<
Martin
I don't like unvented cylinders for many reasons. The one you gave is more common than what you think. They also require an annual service just to store water, and this alone precludes them for me. They also "typically" do not operate at high pressures as a heat bank can. Large bore pressure relief pipes are needed too. And the relief pipe can drip more often than you may want (a London borough replaced all its unvented cylinders because of the constant dripping on the pavements below. They also have a far higher risk of explosion than vented systems. http://www.waterheaterblast.com
A thermal store or heat bank is about the same price and much superior all around, and can supply the CH using TRVs all around, and eliminate boiler cycling.
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Aidan wrote: Janet Bale wrote:
Heatrae technical help have offered an explanation for the bubble loss and suggested a fix.
Could you tell us what that is, please? Thanks
The Megaflo feeds the hot water system in a holiday rental barn conversion. The cold water is all at mains pressure, hence the system is not balanced. There are three shower mixers and other mixer taps. Heatrae suggested that one or more mixers were bleeding cold water across to the hot water system thus raising the pressure in the Megaflo to the point where the inlet valve blows at 8 bar and a reverse flow occurs with hot water pouring down the tundish. <<<<
Was this discharge continuous when the mixers were in use?
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