external expansion vessel

[retiredengineer]

Hi everyone, I am new to this forum and have already found it very helpful and informative. I hope someone out there can offer me some advice.

I have a Vaillant Thermocompact boiler 628E, approx 7 years old.
I have had problems with widely fluctuating pressure, ie system pressure falling to zero overnight, then when filled through the filling loop and fired up, pressure rising to over 3bar and discharging via PRV.

I have opened the valve on the expansion vessel and water came out. From the very informative posts on this forum, I conclude the expansion vessel is shot and I am planning to fit an additional external one.

From this forum, it seems the best place to locate the expansion vessel, is close to the boiler on the return. To achieve this, I will have to insert a 28mm T piece, reduced to 22mm, and connect this to the new expansion vessel which has a ¾ fitting. Trying to bend 22mm copper to make the connection will be a nightmare.

My question is, can I use a flexible 22mm x ¾ tap connector? If not, are there other similar flexible connectors more appropriate for this?
Grateful for any help/suggestions.

 

[kevplumb]

a lot of boilers use flexis so don't see why not

btw you can reduce the pipe size to 15 or even 10 if you wish it will still work ok

 

[bengasman]

Ch water can get much hotter than tapwater, so if you use a flex, it should be capable of withstanding say 85C

 

[Elkato531]

There is a high probability that the rubber core of the flexi tap connection will be degraded over time by the system additives in heating water.

The expansion vessel can be installed on a 15mm branch as it is just a pressure resevoir and is not part of the circulation path.

 

[retiredengineer]

Many thanks for the prompt responses.

It seems I will be able to use 15mm copper, so that makes life a lot easier.

Thanks again,

 

[Booya16]

Hi all. I know this post is fairly old but was hoping to pick your brains.

I too also have the same boiler and had the same issue. I also re charged the internal expansion vessel after depressurising and felt a little water prior to recharging on the schrader valve. Bled all the radiators etc. Seemed to fix the issue, however I feel that the diaphragm is either degraded due to age or ripped but not sure if it was water was just condensation?

The Vailliant 628E Boiler is 13 years old and part of a Vailliant Vantage unvented cylinder system with its own white external expansion vessel (no issues with the hot water). I always clean the whole system internally i.e including clearing out the dust in the burning chamber annually and get the levels within the flu checked regularly.

The charge seems to be remaining at 1.1 Bar when cool and only goes to a maximum of 1.2 Bar when heating is fully on, hence my assumption on the internal vessel and diaphragm. Ps PRV is fine, no leaks. Any thoughts?

What external vessel do you recommend and what size?

I'd rather not go for replacing the internal vessel.

 

[retiredengineer]

Hi, i bought an expansion vessel from screwfix. I soldered in a 28mm to 15mm reducer in the return feed to the boiler and used 15mm pipe to connect the vessel to the return pipework.

Everthing has been great, no problems since.

Good luck, if you do go down this route, i hope it works for you.


Expansion Vessel 8LtrProduct Code: 71018

 

[St0rmer66]

Hi all. I know this post is fairly old but was hoping to pick your brains.

I too also have the same boiler and had the same issue. I also re charged the internal expansion vessel after depressurising and felt a little water prior to recharging on the schrader valve. Bled all the radiators etc. Seemed to fix the issue, however I feel that the diaphragm is either degraded due to age or ripped but not sure if it was water was just condensation?

The Vailliant 628E Boiler is 13 years old and part of a Vailliant Vantage unvented cylinder system with its own white external expansion vessel (no issues with the hot water). I always clean the whole system internally i.e including clearing out the dust in the burning chamber annually and get the levels within the flu checked regularly.

The charge seems to be remaining at 1.1 Bar when cool and only goes to a maximum of 1.2 Bar when heating is fully on, hence my assumption on the internal vessel and diaphragm. Ps PRV is fine, no leaks. Any thoughts?

What external vessel do you recommend and what size?

I'd rather not go for replacing the internal vessel.

Can you clarify a bit more? I'm not quite sure what the actual problem is if the pressure is staying above 1 bar. No point fitting an external vessel if so!

 

[ScottishGasMan]

See lots of external vessels on flexis, both my potable and CH vessels are on them (on the end of a 15mm pipe run) its not an issue. Many boilers use internal flexi pipes much smaller than 15mm ID for the EV connection.

As long as the PRV is still located in the boilers origional place and terminated correctly then the saftey has not been compromised regardless of how the vessel is fitted.

Although it is worth noting on systems with slight/moderate sludge, the flexi to the vessel could be very prone to blocking.

 

[ScottishGasMan]

Oh and on another note. Some water discharge from the shreader valve does not mean the vessel is done. As the air is compressed into the vessel from recharging water vapour is also introduced. Many people assume a spray of water means the diaghram in the vessel is torn/burst. most of these when pumped up will hold air pressure fine, in which case theres no need for an externel or replacement internal vessel.