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]

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.