Unvented hot water issue

[hand91]

Hi all!. First post here so bear with me. I have searched for my issue, but i have not found an answer as of yet. I also know that i can't do any work on an unvented system. i just want some ammunition for when the plumber comes round.


We have an unvented system, megaflo cylinder, indirect with boiler, but have a problem with the hot water. So the problem is that hot water comes from the taps only when we open the hot side all the way i.e., all the way to the left and nearly all the way up. Once the hot water reaches the mixer tap, and we reduce the flow slightly (tap down) or reduce the heat (turning tap right slightly) or both even slightly, stone cold water starts to flow when we do this. If we don't open fully, we don't get hot water flow! This is for all taps in the house.We got told that the problem was the pressure reducing valve which is before the cylinder (we have not had it serviced a good 10 years), so we had that changed (old PRV was faulty) with all original parts (3 bar PRV).
This has not solved the issue. Its only the hot water side that has the pressure reduced, cold is still mains pressure to all the taps (could this be the issue? unbalanced hot and cold pressure? should i check my mains pressure and possibly fit a PRV near the mains entrance?)


Maybe there is a blockage somewhere? Cold water inlet? Hot outlet on top of cylinder? There is good pressure from all hot taps though.
I hope this makes sense. Any advice will be amazing. Have you come across something like this before.



Any help will be appreciated!


Hubert.

 

[hand91]

Sorry don't understand how is my post rude, I was being told what I was talking about & I wasn't talking about back flow from appliances but from cat 1 & 2 at mixers.

Easy mistake to make for a non plumber like myself, i whole heartedly apologise for TELLING you what you were talking about. No need to "Er". In any case, i understand now and that is what this forum is about right! So thanks.

 

[chris watkins]

Loads of people tell me what I am talking about (or not), mainly the wife, & most of the time they says its rubbish. LOL
No need to apologise as no offence was taken (or meant for that matter).

Just a word to the wise, if I may hand91, the plumber you employ will hopefully know his onions as well, yes I know we are still around as this forum proves, so please go easy on them just let them do there job, then by all means ask questions but as your post from Thames Water proves it is a large & complex subject which takes a lot of training & experience to fully understand (thats why we get paid so little:smile5 some more delicate souls may take offence at you telling them what you have found on the internet.

Good luck & hope it all gets resolved.

PS
Can recommend these as they can come with both a flow restrictor & single check valve in one unit & would replace the ball-o-fix to both H&C to mixer taps.
Access Valves from Aquaflow Regulators Ltd

 

[hand91]

Thats life eh! I can imagine if i was a plumber, and somebody was hovering over me and lecturing me on my work i to would get a little ****ed LOL. I appreciate its not all that simple. If it were, everyone could play plumber. Will take a look at your recommendation.

Thanks Chris, you've been a great help.

 

[hand91]

PS
Can recommend these as they can come with both a flow restrictor & single check valve in one unit & would replace the ball-o-fix to both H&C to mixer taps.
Access Valves from Aquaflow Regulators Ltd

They don't seem to have an online store. Do you know where we could buy them?

 

[Dotty]

Please behave or I might have to bring out the Stroppy Croppie stick.

As it is you all get the paddle of rebuke.

 

[hand91]

[h=1]There are two basic dangers that unvented systems must address. First is over-pressurisation, caused by a failed pressure reducing valve, or by back pressure, from a faulty mixer valve for example. The other is overheating.[/h]What would be the symptoms of back pressure to the megaflo?

 

[Gray0689]

Get a decent plumber in mate let them sort it for you

Who installed it in the first place?

 

[hand91]

Plumber is coming later this week, but thought i would share this here first. So here is something interesting. I went to all the taps in the house and turned the ball valves off, on all of the cold taps (no cold water flow when tested). Turned hot on in the kitchen fully and after about 30 seconds the was hot water. Then turned down the flow to about 30% and after a few seconds cold water started flowing (even though cold completely shut off to tap). Same for bathroom sink.

Went to loft to see if hot outlet pipe from cylinder had also gone cold, but it was piping hot for the whole length of the loft.

How does that make sense?!?! How is cold water getting into the hot pipes near the sink??? Hot and cold are not connected anywhere are they?? i mean , why would they be?? Does this rule out unbalanced pressure???

 

[hand91]

seems intermittent. just started working fine...we'll see for how long.

 

[chris watkins]

Got a shower mixer ?

 

[hand91]

Got a shower mixer ?

Yup, with a thermostatic cartridge

 

[kay-jay]

Yup, with a thermostatic cartridge

Isolate the supply to the shower and check performanxe at all other outlets.

 

[chris watkins]

As kay says, thats your link & either non-return valves were not installed or have broken & it is back feeding.

 

[hand91]

ok that makes sense. I don't think there are non-return valves installed tbh. Will check.

 

[hand91]

As kay says, thats your link & either non-return valves were not installed or have broken & it is back feeding.

Oh no wait. It does have non return valves inbuilt.
Crosswater Non Return Valve IBNRV | CROSS-IBNRV
The cold side one was changed as it was completely seized and stripped about 2 years ago, but we didn't change the hot side one.
Could this be the culprit of the back feed?

 

[chris watkins]

Sounds like it, got isolation on either of the shower H or C's turn one off & see if the taps all work.
Is it too late to cancel the plumber & pay me instead ? LOL

 

[hand91]

Sounds like it, got isolation on either of the shower H or C's turn one off & see if the taps all work.
Is it too late to cancel the plumber & pay me instead ? LOL

Ha! if this works i will be able to cancel the plumber all together!!! then i will truly be happy!! will try tomorrow. Ill let you know!

 

[hand91]

So good news!!!!! The problem is finally over. Hot water from the taps working as it is suppose to. The hot side non-return valve on the shower was stuck open, letting by cold water into the pipes. Cleaned it and sprayed the spring inside with WD-40 and works like new!!!! Thanks Kay-Jay and Chris Watkins! Will be checking these every so often.

Also fitted a PRV 3bar on the mains, which probably also contributed to the fix, balancing hot and cold pressure. Certainly got rid of the water hammer!!! No flow rate issues to report.

Thanks everyone for your input. Much appreciated. Very happy. Called the plumber off

 

[Best]

That's great & thanks for letting everyone know how it worked out for you!
Fitting the 3bar prv was a very important thing also, as it will balance both waters.
Remember that, as you have found out, all these items that are meant to have the system working properly can actually fail & are not always reliable. Check valves are not perfect. Be sure to have your unvented unit & all its components serviced once a year by a G3 qualified plumber to keep it working properly & safely & give you full warranty on the unit.

 

[frankiemac]

End of the day slightly piped up wrong, if its a megaflo you only balance cold to bathrooms, as you must have direct feed from mains for drinking water/ kitchen sink.

 

[hand91]

End of the day slightly piped up wrong, if its a megaflo you only balance cold to bathrooms, as you must have direct feed from mains for drinking water/ kitchen sink.

Quite right, however normally, ideally you would have a pipe leading to the cold taps in bathroom directly after the PRV (in loft) that is supplied with the megaflo. We did not do this and it would be quite a hassle to do it at the moment. So we put in a PRV under the kitchen sink directly at the mains to get the same, pressure everywhere. Kitchen cold is plumbed in just after this PRV under the sink so it is still a direct feed from the mains, just 1 bar pressure lower. It also solved water hammer that we have been experiencing

 

[Mike Jackson]

End of the day slightly piped up wrong, if its a megaflo you only balance cold to bathrooms, as you must have direct feed from mains for drinking water/ kitchen sink.

Doesn't make any odds where the feed to the kitchen sink comes from as long as it is mains. Good practice to take all cold feeds in the property from the balanced cold as a lot of modern kitchen taps mix in the body and work better with balanced supplies.

The water to the kitchen sink needs to be fluid category 1 and , if correctly plumbed, the balanced cold will still be category 1. There is a check valve after the balanced outlet that prevents back flow of hot into the cold supply.

 

[chris watkins]

Spot on Mike, as ever.