How to top up (recharge) a hot water expansion vessel?

[Guardian Angel]

On the top of the white expansion vessel is a Schrader valve. When I depress the valve, no air comes out which suggests that the cylinder needs recharging. The reason there is no pressure is that I think I let the air escape (doh!) with some cack-handed attempts at trying to top up the vessel. The sticker on the vessel says that the cylinder should be precharged to 3 bar and the max working pressure is 8 bar. I am reasonably confident that there is nothing at fault with the expansion vessel or the Schrader valve.

Dear ahoythere,

As one of the other posters commented, the expansion vessel has nothing to do with increasing pressure to your shower. In an unvented system, the power to your shower is provided by mains pressure. The purpose of your white expansion vessel is to allow water in your hot water tank to expand safely.

There's a good article here which explains thermal expansion and how an expansion vessel works.
Thermal Expansion - Learn About - Watts

I recently watched a plumber service my own expansion vessel which had filled up with water and am happy to pass on my notes on the understanding that I am not a professional and if you attempt the job yourself, you do so at your own risk.

To recharge the vessel with air, you will need to disconnect it. First you need to shut off the water supply. Cranking the hot and cold water shut off valves in your pic should do the trick. Then open the taps at the lowest point of your house to release any water in the pipes.

Remove the expansion vessel from the bracket. Turn vessel upside down (to stop water pouring out) with the braided hose pointing upwards and the valve pointing downwards and undo the nut which attaches hose to vessel.

The vessel will probably contain water, so go to a sink or take the vessel outside and invert it and allow all the water to drain out.

Now you can recharge the vessel using a foot pump or bike pump and a pressure gauge. 3 bar (44 psi) should do. If any air is escaping, your vessel is faulty and will need replacing.

Re-attach the braided hose to the expansion vessel. Re-mount the vessel in the bracket. Turn off the taps you opened earlier. Open the shut-off valves you closed earlier. Good luck, take care and if in doubt, contact a professional.

 

[Best]

Good discription of vessel & its use. That's not totally correct way to recharge the vessel, & sounds like guy didn't know. I would be careful to work at unvented units, as the other safety features must be checked. Also, what if it is installed incorectly? Not rocket science, but not a DIY job either. Don't penny pinch, it needs done safely & legally, for a few quid.

 

[Guardian Angel]

That's not totally correct way to recharge the vessel, & sounds like guy didn't know.

Is it any wonder that members of the public come to theses forums wanting to tackle jobs themselves? I paid 'a few quid' and yet you say that the plumber may not have done the job correctly. What am I to think?

The problem with the plumbing profession - like so many of the trades - is one of trust. This forum encourages people - like ahoythere - to engage a professional. From our perspective, employing a professional often feels like a lottery! And reading some of the previous comments posted on here (which appear to have been removed), I can understand why people despair of hiring anybody! We hand over our money and have no idea whether the job is being done properly.

Best - in the spirit of Christmas, why not explain to the readers of this post what you would have done differently, thereby helping to raise the level of confidence in your profession?

 

[billybob150811]

i agree with beat why remove the vessel from its bracket adding air is possable in situ the actual pressure should relate to the pressure in the house not to makers norm

 

[ahoythere]

Thank you Guardian Angel. Very helpful.

I note billybob150811's comment about the actual pressure inside the vessel being less than the amount mentioned in Guardian Angel's post and am interested to understand why it would be less than the manufacturer's 'pre-charge' level. The sticker on my VAREM/Extravarem expansion vessel says 'Precharge 3 bar' and 'Max working pressure 8 bar. There obviously needs to be some air in the vessel to prevent it from totally filling up with water as the water in the hot water tank expands. I can sort of see that even very low pressure (room pressure even) would be enough to inflate the diaphram and provide resistance to incoming water, but my knowledge of Boyle's Law and thermodynamics ends there.

 

[dontknowitall]

... but my knowledge of Boyle's Law and thermodynamics ends there.

Plumbers know Boyle's Law, themodynamics, sod's law, murphy's law, consumer credit act, sales of goods act, building regulations, etc, etc, etc.

 

[Best]

Best - in the spirit of Christmas, why not explain to the readers of this post what you would have done differently, thereby helping to raise the level of confidence in your profession?

I can't " raise the level of confidence " in the plumbing profession, merely by giving exact details of how I would do the work. I also want everyone to have a safe Xmas, whether they like what we say, or not. Just surprised that the vessel was removed, as not necessary, but the engineer may be doing a good job. You wouldn't expect a doctor to give advise over the phone, that could mean you risking your or someones life, would you? If anyone asks me advice, I prefer to check it myself for free, rather than hope it is all safe.

 

[secret squirrel]

To post or not to post that is my question.........

Tell me how to do it, pleeeeaaaasssseeeee,

I have read all the posts and every now and again a poster asks a question and is given a very polite reply that it is dangerous to do this wrong, my/our advice is to get a professional in. The original poster not given the answer they want decides that they'll try again. Then replies start back and forth normally ending in "plumbers blah blah"

Last unvented I dealt with was messed around with by a diyer oh and a plumber. The result me turning it off and spending a fair bit of money putting it right.

I normally get bored following these posts but its a cold Saturday afternoon,

Sometimes users of the forum and the public in general have to accept that a professional is the right way to go.

 

[billybob150811]

this is getting a little lost the pre-charge of 3 bar could well be nitrogen as this is less lightly to create rust than air which contains water the pressure reducing valve is usually set to 3 bar so you can gather these are the same if the incoming main is 2 bar the prv isnt called into play and you could reduce the charge, so the pre charge is at the max pressure if the pressure in the exp vessel isnt aligned to the system pressure the expansion force is directed towards the system fittings eg float valves and the exp vesssel is too hard it doesnt do its job so you need to know where you start from you need to know the system pressure the max pressure figure is necessary because there is a check valve in the combined valve and the pressure spikes can be high (water can surge forward but not back into the main) pressure cannot be increased its constant and messing with any of these fittings serves no purpose

 

[fuzzy]

Firstly, may I say this: there is quite a bit of info available on the web - including a YouTube video - about how to top up the pressure in a heating expansion vessel (and I know how to do this), but nowhere can I find any information about how to top up the pressure in an expansion vessel which regulates hot water pressure (to showers, taps etc). I am hoping that this forum will shed light on the subject and that the world will thank me...and you! 🙂

To my problem...

I'd like to increase the pressure to my shower. My house is fitted with an unvented heating system. There is a white 'Varem' (Extravarem 12 litre) expansion vessel located just above my hot water cylinder (picture attached). [To avoid confusion, there is also a red expansion vessel fitted near the hot water cylinder which is not the subject of this post].

On the top of the white expansion vessel is a Schrader valve. When I depress the valve, no air comes out which suggests that the cylinder needs recharging. The reason there is no pressure is that I think I let the air escape (doh!) with some cack-handed attempts at trying to top up the vessel. The sticker on the vessel says that the cylinder should be precharged to 3 bar and the max working pressure is 8 bar. I am reasonably confident that there is nothing at fault with the expansion vessel or the Schrader valve.

Please could someone explain how I go about recharging the expansion vessel and how much pressure to put in it. When I tried to do this earlier, I closed off the two red handles marked 'Hot Water Stop Valve' and 'Incoming Water Main Stopcock' (see picture attached), opened all the hot taps in the house, but still found it impossibly difficult to pump air into the vessel. I'm obviously doing something wrong!

I have taken a couple of photos showing the expansion vessel and the hot and cold cut-off valves and would be very grateful for expert advice.View attachment 4485View attachment 4486View attachment 4485View attachment 4486

ever blown up a balloon?

 

[fuzzy]

Is it any wonder that members of the public come to theses forums wanting to tackle jobs themselves? I paid 'a few quid' and yet you say that the plumber may not have done the job correctly. What am I to think?

The problem with the plumbing profession - like so many of the trades - is one of trust. This forum encourages people - like ahoythere - to engage a professional. From our perspective, employing a professional often feels like a lottery! And reading some of the previous comments posted on here (which appear to have been removed), I can understand why people despair of hiring anybody! We hand over our money and have no idea whether the job is being done properly.

Best - in the spirit of Christmas, why not explain to the readers of this post what you would have done differently, thereby helping to raise the level of confidence in your profession?

thyere would be trust if we stuck with traditional 7 year apprenticeships like the old days, we dont do that anymore and with so many inexperienced fast trackers as genuine and willing as they are you will always get different levels of abilities

 

[BLOD]

I know a landlord that had a flood in one of his flats, when he tried to claim for the damage on his insurance he was asked to provide proof that any work carried out on his unvented cylinder had been done by a plumber with his G3 ticket.
In this case it wasn't a problem and they paid up, but were obviously looking for a reason not to pay !
Could have been a different story !

 

[ahoythere]

Billybob150811 - thanks for the explanation above.