Hi All,
I've an Ariston SX20, but am sure that most combi-boilers
will produce the same symptoms, and be cured
in the same relatively simple manner.
I was losing pressure ... until tonight it was
a top-up with the filling loop every morning and night.
I initially went along with the idea of a leak,
but finally several symptoms pushed me
in the direction of investigating the
expansion tank in the boiler itself.
The symptoms:
************
From a top up every few months,
the intervening period came shorter and shorter.
A top-up used to take up to ten seconds,
it now pressured up almost immediately.
On firing up the central heating the pressure
would increase drastically from the advised 1.0 bar;
until it finally opened the safety pressure release valve.
************
Had a word on the phone with my friendly local
plumbing spares supplier and he told me what
would be required to re-prime the expansion tank.
On the way home tonight I popped into Halfords
and bought a high volume bicycle pump suitably for a BMX. £6.50.
(There are two main sizes of bicycle valve,
the Ariston uses the larger, and I was advised
that most boilers are standardised in this)
Imagine the expansion tank with a diaphragm
laid across its central axis. One half should be filled with air.
In my case, the air had vanished during the six years of its operation,
much in the same way that a car tyre loses air pressure over time.
In this scenario, as soon as the boiler fires up,
because the expansion tank is already virtually full of water,
the water in the sealed system has nowhere to expand to.
As previously stated,
on firing up the boiler, the pressure
would increase drastically from the advised 1.0 bar;
until it finally opened the safety pressure release valve.
In the case of the Ariston SX20, the priming valve
is situated at the back of the boiler.
There is no need to take the cover off the boiler,
it will be seen on the right hand side of the tank,
when looking from above;
hopefully with the original dust cap still on it.
The expansion tank in this model has a capacity of seven litres.
Ariston manual is available as download from...
http://www.centralheating.co.uk/ind....memberDetail/con_id/6444/directoryGroup/5344
...but it doesn't help with this problem.
Here's how I managed the tricky bit:
1. Find the nearest system drain valve, attach a short hose
and place a container at least 4 litres capacity under it.
2. Remove dust cap and attach the bicycle pump to the tank valve.
3. Start pumping the pressure up, until it reaches 1.5 - 2.0 bar.
4. Drain the system a little until the pressure approaches zero.
5. Repeat 4 and 5 until there are approx 3.5 litres
in the container under the system drain valve
(or however much you decide upon for your make of boiler).
6. Leave the pressure primed up to 1.0 bar.
7. Quickly remove the pump so that
not too much air is lost through the valve.
8. Replace the dust cap.
Here I was, thinking this was going to be as expensive as it gets.
P.S. This is all your baby,
I'm offering no guarantees;
suffice it to say that it worked for me.
Happy householding.
John.
