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.

 

[Gray0689]

15mm??? The mains to cylinder should be 22mm

 

[kay-jay]

Ps:

mixer tap tap fault is ruled out as its happening throughout the house.

Nope. Not entirely true.
Opening any outlet when there is a knackered mixer can see the same results everywhere. It will just take a few seconds longer.

 

[hand91]

15mm??? The mains to cylinder should be 22mm

Yes, 15mm from inlet to ceiling height, then it goes into a 22mm , all the way to the cylinder.
We are thinking of doing an extension in the next 2 years or so and we will have the lead inlet pipe changed, and get rid of the 15mm for a 22mm.

 

[wiggers]

I have just got my G3 yesterday so I'm still learning , hand you say you've bought a reliance adjustable prv is this compatable with your cylinder, I may sound too cautious but is buying parts from eBay wise as safety is paramount on these cylinders?

 

[hand91]

I have just got my G3 yesterday so I'm still learning , hand you say you've bought a reliance adjustable prv is this compatable with your cylinder, I may sound too cautious but is buying parts from eBay wise as safety is paramount on these cylinders?

I totally understand where you are coming from. I don't know if you have ever seen or used Unvented Components Europe, but as the name states they sell parts for unvented systems. It just happens that they have an eBay store as well. Its not like I'm buying something from a randomer. On their website, they show the compatibility for many cylinder brands including mine. After a bit of research, using their site and contacting Hetrae Sadia, i have bought compatible parts, including original cold water combination kit which replaced the old one (see links to pics in above posts) at a fraction of the price than i would have from Baxi, or through my plumber!

Apologies if i come across as arrogant, i don't mean to be, nor do i claim to be more knowledgable than you. Also congratulations on getting you G3!

 

[Best]

But you shouldn't be working on any parts of your unvented unit unless you have a G3 ticket!
An extra prv on the mains may be exempt from that if it has nothing to do with the unvented unit & it's safety.

 

[chris watkins]

I have just got my G3 yesterday so I'm still learning , hand you say you've bought a reliance adjustable prv is this compatable with your cylinder, I may sound too cautious but is buying parts from eBay wise as safety is paramount on these cylinders?

Good to be cautious wiggers but they are adding this to the cold water system before the unvented & not removing the one supplied with it, so G3 not effected.

The problem will be that with only a 1/2" bore the flow rates to both system will be dramatically reduced with the drop in the pressure combined, the mains may not now be able to supply all the fittings in the house with the required flow rates.

The problem with the splashing from the taps could be solved by the installation of flow restrictors to reduce the amount of water (not the pressure).

It should also be noted that the installation of single check valve to both the hot & cold supplies to a mixer tap is a legal requirement under the Water Regulations 1999.

The above are exactly why I suggested calling a Plumber in who has there Water Reg's & G3 to the OP. It is very easy to obtain fitting & even install them now days but not so easy to understand the full implication of your actions & lack of full understanding of the subject. WADR

 

[hand91]

But you shouldn't be working on any parts of your unvented unit unless you have a G3 ticket!
An extra prv on the mains may be exempt from that if it has nothing to do with the unvented unit & it's safety.

Just to be clear, i have not done any work on the unvented myself (as i stated in my very first post), always a G3 plumber. I have merely bought the parts.

Good to be cautious wiggers but they are adding this to the cold water system before the unvented & not removing the one supplied with it, so G3 not effected.

The problem will be that with only a 1/2" bore the flow rates to both system will be dramatically reduced with the drop in the pressure combined, the mains may not now be able to supply all the fittings in the house with the required flow rates.

The problem with the splashing from the taps could be solved by the installation of flow restrictors to reduce the amount of water (not the pressure).

It should also be noted that the installation of single check valve to both the hot & cold supplies to a mixer tap is a legal requirement under the Water Regulations 1999.

The above are exactly why I suggested calling a Plumber in who has there Water Reg's & G3 to the OP. It is very easy to obtain fitting & even install them now days but not so easy to understand the full implication of your actions & lack of full understanding of the subject. WADR

Very helpful information. I will definitely be passing this on to my plumber. As i said, i am the type of person who needs ammunition when talking with people working on my home. Second opinion never hurt nobody

 

[hand91]

Chris Watkins, are you saying that having two PRVs (one on the inlet, one before the Megaflo) will have a greater effect on the pressure? Even though they are set to the same pressure?

or do you mean the 1/2 inch (is that 15mm?) diameter of the mains inlet will reduce the flow rate or pressure?

or both?

Can you please explain. A little confusing for me.

 

[Reg Man]

Any additional valve's, will cause a flow restriction, especially as the mains water pipe is undersized. Ideal situation is to have a minimum 22mm main with one PRV and take the cold after the PRV.

 

[hand91]

http://www.thameswater.co.uk/tw/com...w-water-supply-regulations-guidance-notes.pdf

The link shows the check valve regulation you where talking about chris (page 5).

 

[hand91]

Ok cool, that makes sense. Much appreciated

 

[chris watkins]

http://www.thameswater.co.uk/tw/com...w-water-supply-regulations-guidance-notes.pdf

The link shows the check valve regulation you where talking about chris (page 5).

Er, no it doesn't.
I was referring to R15.13.2

 

[DrainMedic]

Oh dear. Someone's found a whole load of rudeness!

 

[chris watkins]

Oh dear. Someone's found a whole load of rudeness!

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.