OK, so am I missing something here? I fix a leak and another appears..

We've two system boilers that run in parallel for some reason. Vaillant
thermocompacts - both of them - about 10 years old now.

One stopped working yesterday. Took cover off to check the flue sensor
and noticed a the hot water output from the H-ex was weeping on both
boilers. One obviously had been doing it for a while (rusty bottom!)

Bought the correct, official "packrings" (o-rings by any other name) and
replaced them.

Put water back in.. the input side leaks on one of them... Took it all
apart, replaced both of those.

Put water back in. The PUMP connection starts leaking.. ON BOTH
BOILERS.. Replaced the packrings (same one - lucky I had to buy a pack
of 10!)

Put water back in. The pip next to the pump is now leaking ON BOTH BOILERS.



Is this just coincidence (combined with 10-year-old boilers)? Are these
packrings all failing, in the same order, at the same time? Or is it,
say, because the boiler has been cold and empty of water, which is
causing pretend-leaks that will go away if I fill it (with bucket handy)
and run it to temperature?

It's too cold for this!

On Jan 18, 10:40*am, Andrew Baker wrote:
OK, so am I missing something here? I fix a leak and another appears..

We've two system boilers that run in parallel for some reason. Vaillant
thermocompacts - both of them - about 10 years old now.

One stopped working yesterday. Took cover off to check the flue sensor
and noticed a the hot water output from the H-ex was weeping on both
boilers. One obviously had been doing it for a while (rusty bottom!)

Bought the correct, official "packrings" (o-rings by any other name) and
replaced them.

Put water back in.. the input side leaks on one of them... Took it all
apart, replaced both of those.

Put water back in. The PUMP connection starts leaking.. ON BOTH
BOILERS.. Replaced the packrings (same one - lucky I had to buy a pack
of 10!)

Put water back in. The pip next to the pump is now leaking ON BOTH BOILERS.

Is this just coincidence (combined with 10-year-old boilers)? Are these
packrings all failing, in the same order, at the same time? Or is it,
say, because the boiler has been cold and empty of water, which is
causing pretend-leaks that will go away if I fill it (with bucket handy)
and run it to temperature?

It's too cold for this!

As pipes heat and cool, expansion puts a lot of stress on the pipes
depending on the layout.
Could be these effects causing your leaks.
They may have been piped up in a poor way, ie without regard to
expansion stresses. Especially in larger systems.

Sludge accumulations can cause local overheating/stresses too in the
heat exchangers.

Two boilers is a good thing for fuel efficiency if they are piped up
correctly.