external pressure vessel

[daffouk]

I need to either replace or fit an external pressure vessel to my boiler. As the internal PV is fitted in the rear of the boiler and would require removing it from the wall, I am opting to fit a new one external to the boiler in the return pipe.

Two questions:

How near to the boiler does the PV need to be fitted?

As I intend to extend the number of radiators in the future, can I fit a larger vessel now, to allow for the increased volume of water. In other words, can the vessel be too large?

Thanx

 

[Bambergaspipe]

I need to either replace or fit an external pressure vessel to my boiler. As the internal PV is fitted in the rear of the boiler and would require removing it from the wall, I am opting to fit a new one external to the boiler in the return pipe.

Two questions:

How near to the boiler does the PV need to be fitted?

As I intend to extend the number of radiators in the future, can I fit a larger vessel now, to allow for the increased volume of water. In other words, can the vessel be too large?

Thanx

3 answers: 1. The expansion vessel in your current boiler is sized to take your current heating situation.




2. You will not be able to extend the number of radiators by adding a larger expansion vessel, you will have to get a bigger boiler, It`s beyond you, get an expert

can`t find 3.

 

[Dan Robinson]

What make and model boiler do you have?

How many rads (and how big) are we talking?

The vessel can't be too large, it can go on the return as close to the boiler as possible, although if the one in the boiler is still working I wouldn't panic about it too much.

 

[Master of None]

I need to either replace or fit an external pressure vessel to my boiler. As the internal PV is fitted in the rear of the boiler and would require removing it from the wall, I am opting to fit a new one external to the boiler in the return pipe.

Two questions:

How near to the boiler does the PV need to be fitted?

As I intend to extend the number of radiators in the future, can I fit a larger vessel now, to allow for the increased volume of water. In other words, can the vessel be too large?

Thanx

3 answers: 1. The expansion vessel in your current boiler is sized to take your current heating situation.




2. You will not be able to extend the number of radiators by adding a larger expansion vessel, you will have to get a bigger boiler, It`s beyond you, get an expert

can`t find 3.

I am only a diyer bamber so don't jump on me.
But...
1. How do you know that?
2. The smallest combi's are around 24kw. So DHW is usually the deciding factor, Not heating output.
Also if the op is asking this question his internal EV is probably goosed and while he would have to get in a RGI to remove boiler and replace internal EV. He is probably competent enough to fit an external one on return to boiler himself. And the part would be a lot cheaper than calling out an RGI and possibly helper if its a heavy boiler. As for size, Unless its a mansion and the one in the boiler is undersized (unlikely as the RGI who fitted the boiler originally should have known this) he could fit one the same size or larger to accommodate for future.

PS if you do fit an external one in this situation. Don't be tempted to put an isolator between this and pipework incase it is accidently isolated and lead to over pressurization. although in commercial plant rooms I always design in a Lockable isolator and drain point for maintenance this is because there would be too much water to drain down to change it and there is more than one EV.

 

[Slugbabydotcom]

Compact boilers usually have an expansion capacity for a maximum of 10 rads but have a heating capacity for more.
There are sizing tables in most Manufacturers instructions
In a domestic environment I find that an 8 litre vessel is adequate for most systems. If there are 8 or more rads often I will fit a 12 litre vessel but take into consideration the size of the rads and take the likelihood of any proposed or possible extensions.

Water isnt clever enough to know where its expanding to or have a preference. Even though it is common practice to fit the PV near to the boiler you may fit it anywhere you like so like as there is a free way for the water to expand into it.

I do fit an isolation valve unlike most others on here but I do make it difficult to access. If the screw part of the valve points downward or to the wall an average tamperer would not know it was there. Apart from that any excess pressure will blow out of the PRV just like it did before you fitted the PV.

Screwfix is a good place to get the PV, you will need a ¾"BSPF X 15mm straight or bent connector and a fixing band and bracket. For some reason these are at a different place in the book.
BES is another good supplier

 

[Bambergaspipe]

I am only a diyer bamber so don't jump on me.
But...

PS if you do fit an external one in this situation. Don't be tempted to put an isolator between this and pipework incase it is accidently isolated and lead to over pressurization. although in commercial plant rooms I always design in a Lockable isolator and drain point for maintenance this is because there would be too much water to drain down to change it and there is more than one EV

.


Yeeawwwn, doo well for Diyer...

 

[Master of None]

I am only a diyer bamber so don't jump on me.
But...

PS if you do fit an external one in this situation. Don't be tempted to put an isolator between this and pipework incase it is accidently isolated and lead to over pressurization. although in commercial plant rooms I always design in a Lockable isolator and drain point for maintenance this is because there would be too much water to drain down to change it and there is more than one EV

.


Yeeawwwn, doo well for Diyer...

Bamber,
I do have some understanding of heating systems. When it comes to domestic plumbing in my own house I am a DIYer and would not expect to be more knowledgeable than the Professional domestic installers on this forum. However in my spare time, ie. at work I am a Heating, cooling, electrical, Ventilation and process building services coordinator / designer.

 

[Bambergaspipe]

I am only a diyer bamber so don't jump on me.

OK.

1Also if the op is asking this question his internal EV is probably goosed and while he would have to get in a RGI to remove boiler and replace internal EV. He is probably competent enough to fit an external one on return to boiler himself. And the part would be a lot cheaper than calling out an RGI and possibly helper if its a heavy boiler. As for size, Unless its a mansion and the one in the boiler is undersized (unlikely as the RGI who fitted the boiler originally should have known this) he could fit one the same size or larger to accommodate for future.

So in your world adding a larger expansion vessel will enable your client to add more radiators, that what you sayin`fool????

 

[Master of None]

Look at the facts that we don't have bamber,

Size of boiler.
Model of boiler.
Size of EV.
Condition of EV.
Volume of system.

Now the OP said that he either had to REPLACE the internal EV or FIT an external EV. This would suggest to me he is actually saying the internal one is faulty. Why would he want to replace like for like if it was undersized. Fool.

I would suspect without knowing the KW of his existing sealed system boiler or the size of his house that it would be possible to add a few more rads (unless the RGI who fitted it originally got the job by pricing the very smallest and cheapest on the market) providing things like pipe size and expansion is adequate. Fool.

If he is going to add an external EV why not oversize it a bit compared to the current internal one, considering we know nothing about the installation. Fool.

PS.
I don't really think you are a fool. And you don't know that I am.
But you hit me first etc.

 

[daffouk]

Thank you to all, but especially Dan_Robinson, Master of None & Slugbabydotcom.

You have indeed answered my two questions.

As you surmise, my current internal PV is knackered, i.e oozes water when the schrader valve is pressed : sorry I thought I intimated that.

The boiler is a Ideal Isar HE30, i.e. 30kW (don't tell be how bad they are, I know only too well, I have to buy it fixerators every three weeks, see I do know the technical terms for the devices in the system)

The current size of the EV in the boiler is not quoted, but I would assume around 8 litres, and yes it is infinately easier to put in an external PV as I would have to demolish half the external wall to free up the flue before the unit would come off the piping frame. I'm all for the easy option at present as I want to keep the idiot of thing going till the summer when I intend to have it replaced. (not with another un-ideal boiler)

The current volume of water in the system I estimate to be 120 litres and once I include the new pipework and radiators in my extension it will increase to 200 litres.

Multiplying the vol by the magic figure of .074 gives the size PV I need as 15 litres.
Toolstation, who I prefer to Screwfix as they tend to have things in stock, do a 12 litre or an 18 litre so I would err on the side of caution and get an 18 litre.

and yes I am quite capable of plumbing in a PV. I was wiping lead joints long before some plumbers could hold a tap spanner, still have the tallow ingrained in my hands to prove it!

And fear not everyone, I won't put an isolation valve in the pipe to the PV, afterall what's wrong with a freezing kit if I need to replace it in the future!

Wow, that was a lot of words!

Cheers, Dave

 

[Dan Robinson]

Good luck...