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?