re-pressuring my boiler

[tim...]

Had to re-pressure my boiler today (Baxi something or other)

never, in six previous (Gas CH) properties have I had to do this before.

Is this symptomatic of a wider problem or just bad luck?

TIA

tim

[clive.r.long]

Hi,

I had a new boiler fitted recently and the plumber said to me "if you can't pressurise the system, or the pressure continually drops, you are going to have to find the leak"(*). We discovered the truth of that statement today as a new rad was put in.

Clive

(*) From your post, I think you suspect this is the siutation you face.

[Chris Hogg]

I had a similar problem about 12 months ago, after 15 years of hardly ever having to adjust the pressure. At about the same time, SWMBO noticed a light brown stain on the sitting room ceiling (it's a bungalow). On investigating, one of the brass automatic air bleeds in the loft above the stain had developed a leak around the screw threads on the brass cap (not the little air-release knob on the top), with a crusty greenish deposit, suggesting internal corrosion. Got some Fernox F4 leak sealer* and injected it into a radiator. Leak sealed over the next few days. Got a new pair of air bleeds with the intention of replacing both old ones (feed and return) in the Summer when CH not in use, but family illness and bereavement meant it never happened - perhaps this Summer! Meanwhile the Fernox is still doing a good job.

Might be worth a try if your problem persists.

• Other, cheaper leak sealers are available.

[David]

The water is going somewhere. The question is, "Where?".

Could be a pressure relief valve, could be a leaking joint anywhere in the house. Could be a fault in the boiler, could be totally unrelated.

Time (and possibly damp patches) will tell.

Best of luck.

Dave R

[Chris Bartram]

Depends how often. If it's more than once in a blue moon you may have a problem. If there's no visible leaks, check the pressure relief valve by putting a poly bag over the outlet. Also check the expansion vessel- if the pressure rises a great deal when hot, that's probably at fault, and the high pressure opens the relief valve.

[Roger Mills]

It could be a one-off, so I wouldn't panic immediately.

But I *would* monitor the pressure for a bit several times a day - especially when the system is heating up from cold.

If you keep having to top it up, you need to investigate. There is either a leak, or there could be a problem with the expansion vessel - causing the pressure to rise above the point where the pressure relief valve dumps some of the water. When the system cools, the pressure will fall again - probably below a safe level, and will need topping up. If this *is* the case, the problem with the expansion vessel needs to be fixed - either by replacing it, or it may just need to have its air side re-pressurised.

[Adrian Caspersz]

All the stories about re-pressurising heating pipes, filling loops(?) and finding leaks has put me off getting such a system as a replacement. Ours is a vented gravity system, the replacement will be the same me thinks.

Unless there is some huge benefit I'm missing?

[spuorgelgoog]

An unvented primary system can only lose the water in the system, in the event of a leak.

A vented primary system with a header tank connected to the mains can lose water indefinately.

This is a big difference if there is a leak while you're away.

An unvented primary system also removes the loft header tank with its potential for ball valve faults, problems with pumping over or drawing air into the system, etc.

Owain

[harry]

The reason is cavition. Which becomes a bigger problem with narrow waterways and exotic metals. As in new installations. Cavitation reduces efficiency and causes erosion in the system.

The best way to overcome cavitation is with higher system pressure than can be acheived with gravity (esp. in bungalows)

[Harry Bloomfield]

harry formulated the question :

I have seen the result of cavitation erosion on ships propellers and water authority large pump impellers, but never on a CH pump.

[Martin Bonner]

Were the previous systems pressurized, or was there a header tank. If they weren't pressurized, that would explain why you haven't had to re-pressure them :-)

Once every six months: neither - that's just how they are (like bleeding radiators occasionally).

More often that that: Symptom of a bigger problem (not necessarily a *much* bigger problem). (Also like bleeding radiators.)

[Martin Bonner]

Filling loops are theoretically temporary bits of plumbing which are actually completely permanent. They aren't any sort of problem.

Re-pressuring is no more complex than bleeding a radiator (easier actually).

At least with a pressurized system you *know* the thing is leaking slowly. with a header tank, you don't find out until you notice the damp patch, or the joist fails through rot.

At least as easy to operate. Much less water to leak. No need for a CH header tank in the loft which can freeze.

I get the feeling that most systems are pressurized these days, so you may reduce your choice.

[harry]

All wear/erosion involving clean moving liquids is down to cavitation. Even clean cold water running over stones and concrete.

What else is there to cause wear on say valve seats?