Pressure Issue

BryanG

Hi,



I have a burnham IN4 gas fire boiler with probe cutoff and the intermittent style pilot (i.e. non-standing pilot). It's basically brand new and been working great however my wife accidentally shut off the heat rather than turning down the thermostat so we came home to a cold house (51F). In the process of heating it back up I notice when the pressure in the tank gets to about 2 PSI it cuts out as it should based on where the presterol gauge is set....when it drops psi it comes back on. Normally about a cycle per 2 minutes or so. My question is, is this normal based off how far the temp needs to come up or do I have a venting issue? If this is not normal than my thought is the main vent needs to be replaced.



Thanks for the help,

Bryan

Jamie Hall

If it only does this

when coming back from a really big -- if accidental! -- setback, it's not a problem.  Most steam systems have boilers which are slightly oversize; when the radiation is full and condensing as much steam as it can, the additional steam from the boiler builds pressure and the boiler cycles off.  Then cycles back on when the steam condenses.  And so on, until the thermostat is happy.



If it does this on a normal heating cycle, then yes it is a venting issue.  But it doesn't sound, from your description, that that is the case.

BryanG

Awesome.....

Thanks for your help Jamie, I'll keep an eye on it

nicholas bonham-carter

Short-cycling

This is a situation where a low-pressure 0-3 psi gauge would show you if you are short-cycling on insufficient main venting, or an oversize boiler. By reading the back-pressure as the boiler starts to make steam, you can see whether the air is escaping with very little resistance, or is having to be forced out of the main vents.

You may have good venting, but an oversized boiler. In the perfect world (not easily obtainable), the boiler would be able to run continuously, until the thermostat was satisfied.--NBC

BryanG

Short Cycling

Thanks, for that. I did end up replacing the main vent as pressure was building on a normal cycle. I also found a radiator at the far end of the system that had a clogged vent which I replaced. The system barely registers any PSI right now on a normal cycle. However you comment does have me slightly concerned about the boiler size. The IN4 is one of the smallest Burnham boilers and based on the BTU output (105k) was in line with the previous burnham boiler. What are some other tell tale signs of too large a boiler even if I'm not short cycling?



And one other question somewhat unrelated, my main vent isn't on much of a nipple at all...less than two inches. Would lengthing the nipple improve venting capacity? I feel like I know the answer to that I just don't know why.



Thanks