CH pressure rises constantly
 

can any of you central heating experts out there give me a clue about
how to solve this problem i'm having ?

why would CH pressure contantly rise if there are no airlocks and not
too much water ?

the pressure reading on my combi boiler slowly rises until about 3
bar, at which point the relief valve opens and releases some water
until the pressure drops, which all seems 'normal' enough, but the the
cycle immediately begins again (pressure rises, relief valve opens,
pressure drops)....and so on.

this all started after i drained the whole system and refilled it
(along with a quantity of corrosion inhibitor).

I know what you're thinking.......AIR in the system!!. This was my
first thought, and i've been bleeding the rads (or attempting to)
regularly since refilling the system, but for the last couple of
months now, i'm getting no more air, so the system appears to be 'air
free' so what do i do now ?

i've checked the filling loop that doesn't appear to be feeding
anything in, so just where is this pressure coming from ?

i'm not an expert in CH systems so i don't know what other things
could cause pressure rises.....i only know about airlocks and too much
water.

marley wrote:
i've checked the filling loop that doesn't appear to be feeding
anything in, so just where is this pressure coming from ?

Check again. Even better, disconnect the filling loop altogether and
see if the problem still occurs (you *should* have a non-return valve on
the filling line so you can do this).

I'd be willing to bet that the isolating valve on the filling loop is
leaking very slightly, which will slowly raise the system pressure. At
least, that's what happened to me.

--
Tony

Yes, what Tony said.

Additionally there are two further avenues of investigation should disconecting the filling loop (which in a any case should not be left permanently connected) not solve it.

1/ water can get in through the secondary heat exchanger in which case you need a new one. To check for this turn off the isolation where the cold water goes into the boiler and see if that stops it. Obviously you have no hot water while you are checking this out.

OR

2/ should this only happen when the system is hot the pressure vessel requires attention. Either the air pressure needs checking, or the membrane is ruptured or it is incorrectly sized for your system in that order.

Start with the filling loop. I usually leave these disconnected when I do a service or installation. Should it be the loop get a good quality replacement.

thanks Tony and Paul for your suggestions, i'll check these out and
post the results.

marley

"marley" wrote in message
...
can any of you central heating experts out there give me a clue about
how to solve this problem i'm having ?

why would CH pressure contantly rise if there are no airlocks and not
too much water ?

Only one reason - there is water being introduced from somewhere!


the pressure reading on my combi boiler slowly rises until about 3
bar, at which point the relief valve opens and releases some water
until the pressure drops, which all seems 'normal' enough, but the the
cycle immediately begins again (pressure rises, relief valve opens,
pressure drops)....and so on.

this all started after i drained the whole system and refilled it
(along with a quantity of corrosion inhibitor).

I know what you're thinking.......AIR in the system!!. This was my
first thought, and i've been bleeding the rads (or attempting to)
regularly since refilling the system, but for the last couple of
months now, i'm getting no more air, so the system appears to be 'air
free' so what do i do now ?

Well I wasn't thinking air at all.


i've checked the filling loop that doesn't appear to be feeding
anything in, so just where is this pressure coming from ?

To check your filling loop disconnect it and place a receptacle under the
fill valve from the cold water main. If it drips in at all you have a source
of a slow pressure rise. Either shut off the valve properly or change it. In
any case the filling loop should be disconnected while not in use
specifically to avoid this sort of problem.


i'm not an expert in CH systems so i don't know what other things
could cause pressure rises.....i only know about airlocks and too much
water.

There is another and more costly failure which can cause pressure rise - a
pinhole leak between mains and heating circuit in the boiler secondary heat
exchanger. You can check this after you have eliminated the filling loop as
above by turning off the cold mains inlet to the boiler and open a hot tap
which will depressurise the mains water circuit through the boiler. If the
heat exchanger is the culprit the pressure rise will cease. You then need to
replace the secondary heat exchanger.

What model of boiler is it anyway?

There is another and more costly failure which can cause pressure rise - a
pinhole leak between mains and heating circuit in the boiler secondary heat
exchanger. You can check this after you have eliminated the filling loop as
above by turning off the cold mains inlet to the boiler and open a hot tap
which will depressurise the mains water circuit through the boiler. If the
heat exchanger is the culprit the pressure rise will cease. You then need to
replace the secondary heat exchanger.

What model of boiler is it anyway?



It's a Worcester Bosch 24 Si II combi, fitted summer 2003