pressure fluctuations and boiler failure

[RobertL]

When the Vokera man serviced my old boiler I asked him what conditionthe 20 year old heat exchanger was in. he said it was fine and he told me the usual reason the heat exchangers failed was because of pressure fluctuations gradually causing metal fatigue as the thing flexed. When people let the accumulator run out of air the fluctations got bigger (hot/cold expansion) leading to rapid fatigue and failure.

So this set me thinking - would it extend the life of the heatex to add a bigger accumulator to reduce the hot/cold pressure fluctations?

has anyone else heard this or is it another urban myth that these repairmen tend to carry (the previous guy assured me I shoud leave all the TRVs on maximum all the time for max efficiency).

Robert

[Roger Mills]

I'd not previously heard that one. I would have thought that the stresses induced by heating and cooling the heat exchanger would be far greater than any caused by pressure fluctuations.

[ransley]

What you can monitor is water pressure to be sure its at the minimum to run right, your system only needs enough water- pressure to get out the air and have all water. A boiler repair guy isnt going to spend the time to do it right they just fill it up, I got mine about 40% lower in pressure. At the highest radiator on a cool non running boiler bleed off some excess water. You shouldnt have much pressure fluctuation between cold and hot, maybe 5lb, im in the US, I dont go by bar, excessive fluctuation, or pressure raising way up when running is another issue you dont want. Low pressure =3D low stress

[Harry Bloomfield]

RobertL formulated the question :

It only needs to be big enough to take care of the expansion. The thing is to make sure the diaphragm doesn't burst and that air pressure is maintained.

Wear and tear will be mostly due to heat cycling, rather than pressure cycling - so anything which will help reduce this will improve longevity.

A really bad idea from a fuel economy point of view. How much fuel would need to be wasted, to make the boiler last a little longer and how much do boilers cost?