Replacing expansion vessel on a unvented hot water only storage system (package type)

[thebigred]

Hi,

I have a failed expansion tank (which is full of water and has 0 bar pressure) on my unvented hot water storage system. Currently the pressure relief valve is venting water to the overflow.

This diagram matches what I have:



I want to try and do the job myself if possible but it seems these types of systems are not very common and most plumbers merchants I talk to seem to think I'm talking about a sealed combi system (i'm not, it is a text book unvented hot water system, i've checked the standards doc)

My plan is to do the following:

0. Isolate the mains supply 🙂
1. Drain the system off
2. Remove the expansion vessel and fit a replacement one
3. Remove the pressure relief valve and fit a replacement one
4. Fit a pressure gauge on the pressure reducing valve (There currently isn't one so I've no idea what the pressure is)
4. Make sure everything is tight (although not too tight)
5. Turn the water back on

I guess my questions are:

1) Does the plan above look good and safe

2) I know the vessels come pre charged with about 2 bar, but how do I calculate how much pressure I need in my system?

3) I presume I need to put pressure into the vessel before I put water back into the system

4) The vessel currently in there is a 18L 10 Bar Max one? - Do I need to replace it with another 10 bar max one? Most I can find at merchants and online are only 3/4 bar max? (It's a white Zilmet one model 0036)

5) I've been quote £200-300 by the company that installed the system to do the above job - to me that seems pretty high but I'd welcome any advice - perhaps it's a bargain and I'm being a tight git!

Thanks in advance

Oli

 

[Atouchofgas]

Replacing expansion vessel on a unvented hot water only storage system (package

Do you have your g3 cert ( sounds like you dont ) You need a plumber with g3

 

[thebigred]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

Hi,

Nope I'm a DIY'er I'm afraid! Do I need certs to work on my own system then? (excuse the ignorance there please 🙂 )

 

[stoker122]

Replacing expansion vessel on a unvented hot water only storage system (package

You need to be G3 qualified to carry out this work. £300 sounds a bit high though.
Post for someone local to help in the looking for a plumber section 🙂

 

[thebigred]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

Thanks for the advice will do - much appreciated 🙂

 

[cr0ft]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

A lot of unvented cylinder parts can be quite expensive as the manufacturers often have a racket going on, i.e. buy our parts or we void your warranty...

An example, a manufacturers expansion vessel can cost around £60 alone, before you even factor in the pressure reducing valve and pressure relief valve. They could be another £50 between them easily.

Add on 2 hours labour, around £90 ish and you are already up to £200. VAT on top of labour would take you to £220. Unless there are any difficulties accessing the cylinder to replace parts then that price is around the right amount imo.

 

[lame plumber]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

have a look on u tube to see what happens if you get it wrong🙂

 

[Jordy]

Replacing expansion vessel on a unvented hot water only storage system (package

A lot of unvented cylinder parts can be quite expensive as the manufacturers often have a racket going on, i.e. buy our parts or we void your warranty...

An example, a manufacturers expansion vessel can cost around £60 alone, before you even factor in the pressure reducing valve and pressure relief valve. They could be another £50 between them easily.

Add on 2 hours labour, around £90 ish and you are already up to £200. VAT on top of labour would take you to £220. Unless there are any difficulties accessing the cylinder to replace parts then that price is around the right amount imo.

So you can't fit a generic expansion vessel?

 

[chris watkins]

Re: Replacing expansion vessel on a unvented hot water only storage system (package

Do you have your g3 cert ( sounds like you dont ) You need a plumber with g3

Just for your info G3 refers to Part G of the Building Regulations, under section 3 it states that you have to be competent to work on these hot water systems. You do this by training & passing an assessment, when are normally issued with a card which you can show to customers to prove this.
It makes no difference whether you do the work yourself or someone does the work for you, without this you will be breaking the law, I am afraid & more to the point putting yourself & loved ones in danger.
On the plus side it is likely that the plumber will be able to sort out the expansion safety valve so this may not need changing if it has not been discharging for long.

 

[jim fennessey]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

if you dont want to be another Neil Armstrong visiting the moon without a spaceship,i would not advise working on an unvented boiler,they can be lethal dont put anyone at risk for the sake of a few spondoolies,get a plumber who has got his g3 card.

 

[Killy Bing]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

In plumbing there are qualifications to say you have the skills do something such as basic plumbing blah blah

then you have the likes of g3, the acs (gas), water regs and legionella training.

these ones are aimed at keeping you safe and not killing people and these are the ones that when done as diy can quickly prove fatal.

Unvented cylinders require g3 because they go boom!
expansion vessels are the first line of the safety devices.

 

[Mike Jackson]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

[video=youtube;9bU-I2ZiML0]http://www.youtube.com/watch?v=9bU-I2ZiML0[/video]

 

[lame plumber]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

just keep that vid on file croppie for all diy unvented questions 🙂

 

[Unregistered]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

I have broken exspansion vessel it's started to rust through near the threads that make up the connector. Read some of the comments above. Was thinking of just doing the job diy as it looked as simple as drain the hot water tank and then replace a like for like exspansion vessel to the same connector. There is not other valves to replace. Do you really need a plumber with g3?

 

[Dotty]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

I have broken exspansion vessel it's started to rust through near the threads that make up the connector. Read some of the comments above. Was thinking of just doing the job diy as it looked as simple as drain the hot water tank and then replace a like for like exspansion vessel to the same connector. There is not other valves to replace. Do you really need a plumber with g3?

YES YOU DO!

It is illegal under part G of the buildings regulations, a statutory and enforceable instrument, that anyone working on an unvented system over 15 litres must be proved competent through training and membership of the competent persons scheme.

And you need to register with us too.

 

[Dotty]

Re: Replacing expansion vessel on a unvented hot water only storage system (package t

I just read through the entire thread and I'm astounded you still had to ask!