Fitting external expansion vessel.

[whistler]

I have a Vaillant Turbomax about 18 years old and it looks like the expansion vessel has failed. As the vessel is located at the back of the boiler thus making it a difficult and expensive job to replace, I'm considering fitting an external expansion vessel. I understand that this should be fitted to the return pipe, but it looks pretty awkward to connect to this. The flow pipe looks a much easier option.

Is it ok to pipe into flow pipe? Any disadvantages to this?

 

[Madrab]

It's basically down to the higher heat on the flow, EV's are happier on the return side of the boiler as it's invariably cooler.It just helps to maximise it's lifespan.

 

[ianmcd]

Expansion vessels are supposed to be checked/re-charged every year, bet yours has never been serviced, why do you think it needs replaced ?

 

[Gasguru]

Some boilers check there's sufficient water in the system by reading the water pressure sensor and looking for a change in pressure as the pump starts.
If correct placement of an external vessel is not adhered to the pressure change may not be sufficient.

There should be no issue connecting a vessel onto the flow pipe...the moderate temperature rise not really an issue (could always make the pipework longer/horizontal etc).

 

[whistler]

Expansion vessels are supposed to be checked/re-charged every year, bet yours has never been serviced, why do you think it needs replaced ?

Continually losing pressure.
Water from the air valve when depressed.
Boiler serviced annually over last 15 years.
Vaillant manual recommends 3 yearly check on air pressure.
I think 18 years is good going for a rubber membrane!

 

[ianmcd]

Continually losing pressure.
Water from the air valve when depressed.
Boiler serviced annually over last 15 years.
Vaillant manual recommends 3 yearly check on air pressure.
I think 18 years is good going for a rubber membrane!

bet it just needs recharging properly

 

[whistler]

bet it just needs recharging properly

Do you mean like I did this morning?

You're bound to ask, so here goes

Isolate mains supply
Isolate flow and return
Drain boiler
Leave drain open
Pressurise EV to 0.7 bar.
Close drains
Open flow and return
Repressurise system to 1bar.

Did I miss anything?

 

[oilhead]

If you had water from the Schrader valve before, you will get again. 18 years isn't down to lack of service, more likely that it was not big enough in the first place, and also very close to the heat source. Replace remotely and if on flow, then as much away from the boiler as you can. Once you have some water in the supply, then this will need to heat up completely in what is a dead leg to cause damage to the membrane. I replace many on oil boilers that whilst being on the return still get as hot as the flow through convection. They are also generally undersized as it is the only size that fits in the case.

 

[ianmcd]

Isolate mains supply
Isolate flow and return

dont know why you thought you had to do that, so what happened when you did all that ? did the vessel hold pressure ?

 

[whistler]

dont know why you thought you had to do that, so what happened when you did all that ? did the vessel hold pressure ?

1. Health and safety! Also to prevent the boiler inadvertently trying to fire up with no water in it!
2. To prevent the entire system draining down!

After repressurising the vessel held pressure for a short time then when the Schrader valve was pressed water spurted out. A sure sign that the membrane has perforated.

 

[Gasguru]

You don't normally isolate anything except the power..there's far too high a risk of valves leaking (esp the flow and returns) leading to more cost, all you need to do is bleed the rads and drop the pressure to zero.
Start pumping up the vessel and release more system water as necessary to kept the system down at zero.

 

[ianmcd]

After repressurising the vessel held pressure for a short time then when the Schrader valve was pressed water spurted out. A sure sign that the membrane has perforated.

Is it really ?

 

[MeldrewsMate]

Is it really ?

I think Whistler has this one right. No need to go on at him/her.

 

[whistler]

I think Whistler has this one right. No need to go on at him/her.

Thank you!

 

[oilhead]

I think Whistler has this one right. No need to go on at him/her.

I agree, if water is getting to the Schrader valve, then the vessel is goosed.