Hi Sorry to be a pain for asking 8 in-depth questions, but I cannot be without the boiler as I have
three grandchildren living here (4 years, 3 years and 18 months), so I'm trying to get everything
clear in my mind, and the parts, so I do not have to travel to a
merchants (as I live a fair distance from stores) or wait for a delivery if I get it wrong and put the
boiler out of use for a while.
I have got a problem with the boiler.
I am trying to establish if it's the PRV or the expansion vessel OR BOTH!
My boiler, an Alpha CB28 (LPG) for sometime has been losing pressure. I have been unable to deal
with it until yesterday. I’ve got into the habit of filling up to around 2 bar,
as that gives more time before I have to do it again. At 2 bar with the
central heating on it takes around two hours before it needs refilling.
Without the central heating on it holds it for some time.
I’ve read different posts on what the problem might be.
PRESSURE RELIEF VALVE
I re-seated the PRV yesterday, but that didn’t help. Also the PRV is discharging
below 3 bar – maybe around 2.5 bar.
The PRV was replaced by British Gas around 4 years ago.
EXPANSION VESSEL
The position of this expansion vessel on the boiler is a pig. It is behind the boiler against the wall.
It is going to be impossible to get it out without removing the boiler as the boiler is in a
fitted kitchen cupboard and I cannot get above to look down. I can get to the top and remove the
cover plate, but it seems that the expansion vessel is not positioned at the top, because I can’t feel
it when I force my hand down.
Until yesterday, on YouTube, I didn’t realise that you can replace the “original expansion vessel” with
“another fitted away from the boiler” (making the original redundant).
We’ve been here 10 years so the boiler is probably 15 or 20 years old. I have never
re-pressurised the expansion vessel. We had a service plan with British Gas for around 4 years,
they replaced a lot, including the heat exchanger
(that they were not happy about that because of the cost).
They never said or wrote down that they touched the expansion vessel. So considering the
nightmare to get it out, it seems it will be easier and a lot cheaper to replace with an
external expansion vessel. £91 vs £26
MY QUESTIONS
If you recommend that I need to deal with the “expansion vessel” then I need to confirm a few
points before I start/order the items.
I can't find my boiler manual so I downloaded one.
The download says Natural Gas - whereas my original said natural gas AND LPG but I don't think
there is a difference apart from possible jet sizes (correct me).
The Expansion Vessel Size (pre-charge press.) is 8 L at 0.8 bar
On Screwfix someone having the same problem also had an 8 litre “expansion vessel” but was advised
to fit a 12 litre expansion vessel - he didn't - and fitted an 8 litre and had problems, possibly
due to another problem?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Found this one at Screwfix: Expansion Vessel 8Ltr - Product Code: 71018
(Question 1) Should I replace like for like i.e. 8 litres?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ORIGINAL Expansion Vessel OUTPUT pipe is 10mm.
THE PIPE WORK INSIDE THE BOILER IS 15mm
I cannot see where it goes into BUT the Heating Return Pipe is 22 mm - so the 10mm has to be reduced.
As the internal pipe work is 15mm, I'm assuming that the 10mm (from EV) is fitted
to 15 x 15 x 10mm reducing tee.
(Question 2) There is not much room inside the boiler to cut the 15mm pipe to connect the pipe for the new
expansion vessel - but the 22mm Flow & Return are coming down from upstairs.
So this is what I was thinking of doing - cutting into the return BEFORE it reaches the boiler casing
(i.e. before the 10mm EV original is connected)
The distance from where the original EV is fitted and to where my new join will be, is just over the height
of a regular boiler.
Would this be OK?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
OUTPUT FROM EXPANSION VESSEL
Someone posted that the output of the "Screwfix Expansion Vessel" is: 3/4 inch BSP (male/threaded).
(Question 3) Should I use;
15mm x 3/4" Female Coupling Compression - Diameter: 15mm x 0.75in
OR
22mm x 3/4" Female Coupling Compression - Diameter: 22mm x 0.75in
Does 0.75 = 3/4 inch BSP?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CONNECTION FROM EXPANSION VESSEL TO 22mm RETURN PIPE
As I said before, the original pipe fitted 'from' the expansion tank is only 10mm.
But coming from the new Screwfix expansion
vessel is either 15mm or 22mm and is to connect to a
22mm heating return pipe.
Based on your answer to Q3 above I'll use either;
22mm Reducing Tee 22 x 22 x 15mm
or
22mm Equal Tee 22 x 22 x 22mm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(Question 4) Do I just leave the redundant expansion vessel connected?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The only place I can fit the NEW expansion vessel is ABOVE the boiler, I was thinking
6 inches above the top of the boiler to allow recharging.
(Question 5) Is this acceptable - will is still work OK - or does it have to be inline or below?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(Question 6) Screwfix say that their Expansion Vessels are "charged to 0.8 bar" - but is there
any point where I might have to re-charge it?
I don't have any bicycles pumps here anymore, and if I did how would I know what 0 .8bar is?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A chap on YouTube said it's a legal requirement to always disconnect the filling loop.
My boiler seems to be factory fitted.
(Question 7) Is this true?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Another bloke said on Screwfix - "Expansion vessel diaphragm ruptured in my central heating boiler.
The replacement part was approx £50 + vat. Not a bad price, but the boiler has to come off the
wall and stripped down to fit it.
This handy bit of kit just takes a Tee piece and flexi hose pipe to fit on the return to the boiler,
2 hour job max."
Am I making this to hard for myself? Or is there an easier way - how do you connect FLEXI HOSE PIPE to copper?
Or do you just find the bits and make up to suit?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 22mm flow & return coming down from upstairs are not clipped to the wall, but they are so close to the wall
that I can't get the pipe cutters
behind, so I'll have to use a hacksaw, and then use compression although I'd prefer end feed.
JUST A FEW OF THE BOILER SPECS
ALPHA CB28 (lpg)
Central Heating (Sealed System)
Max. Working System Pressure 2.5 bar
Min. System Pressure 0.5 bar
Max. System temperature 82°C
Pressure Relief Valve Setting 3 bar (44 PSI)
Expansion Vessel Size (pre-charge press.) 8 L at 0.8 bar
Flow Connection 22 mm
Return Connection 22 mm
Relief Valve Connection 15 mm
Recommended System Pressure (cold) 1.0 bar
CH Water Temp. (Approx. max.) 82°C (180°F)
Domestic Hot Water
Max. Mains Inlet Water Pressure 8 bar
Min. Mains Water Pressure 0.2 bar
Min. DHW Flow Rate 2.5 l/min
Mains Inlet Connection 15 mm
DHW Outlet Connection 15 mm
DHW Water Content 24/24X 0.2 L
28/28X 0.24 L
Outlet Water Temp. (Approx. max.) 62°C (144°F)
PLEASE NOTE: My Boiler is NOT 28X (it's a CB28)
Many, many thanks in advance.
Will appreciate any questions you can or have time to answer.
Regards
Stephen
