Vaillant boiler pressure

M.Joshi inscribed thus:

I'm not a plumber but if you are loosing water from a sealed system it has got to be escaping from somewhere. Any joint, soldered, compression or otherwise is a potential source of escape. You should carefully inspect every pipe, starting from one end of the system and working your way round each radiator. Don't forget to check any taps, drains, or bleeds! Any sign of sweat or moisture could indicate your leak! The problem is that moisture very quickly evaporates, particularly if the environment is warm.

Murphy dictates that any leak will be in the hardest place to get at !! Good Luck.

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Best Regards:
                      Baron.

Can you pressurize the system with air while cold? I've used that trick to find leaks in automotive cooling systems. I haven't seen radiators used to heat a house since a few built back in the 1950s but the systems are usually pretty simple.

That's what I'd do. Figure out how to connect a tire valve into one of the system's air vents. Then pressurize the whole thing with a bicycle pump to maybe fifty psi and then go over every joint with liquid soap and look for bubbles. If you can avoid using the plumber's sealant stuff, it would probably be better just on general principles.

It occurs to me that this is the sort of thing I ought to do whenever I do an extensive plumbing job around here: insinuate a Schrader tire valve into the water system somewhere and whenever I think everything's going to be just swell, pressurize it to a good hundred psi with the air compressor and see if it actually is.

M Kinsler

Lots of things going on here, and a lot more information is required in order to diagnose this properly.

How old is the system for one. Not the boiler, but the entire system.

a) What kind of system is this - One or Two pipe? b) Copper or Iron? c) Are there any direct copper-to-iron connections? d) What kind of expansion tank do you have? e) And have you verified the pressure in it if it is a bladder tank, or have you drained it recently if it is a water tank? f) Do you have automatic bleeder valves? If so what kind? g) Do you have an automatic fill valve? h) One, two, three-or-more story application? i) How recent was the boiler installation? j) How long has this been going on? k) If this is a vintage system originally, was it sized for gravity or pump circulator? l) And how big (how many radiators) is the system overall?

In general, how do you like this little boiler? As I understand it, it is a gas-fired, stainless steel, wall-hung condensing boiler?

There does happen to be a recall on some Vaillant boilers, have you checked that? That may be the explanation right there.

DO NOT pressurize the system with air, and most especially DO NOT pressurize to anything near 50#. First you will blow out the TPR valve on the boiler, second, you stand to blow out the gaskets in the heat- exchanger.

If the system is two-pipe, black iron, and sized for a circulator, the leaks will be at-or-around any new installations you may have made or had made. This could include the boiler, the towel-warmer radiator or any other radiators you have installed. It is also possible, but unlikely that recent installations disturbed an existing joint, or a knuckle was disturbed for alignment purposes somewhere within the old piping. This should show pretty obviously.

It is also entirely possible that the system has not been bled properly (assuming you have automatic bleeders) and what you are observing is simply the bleeding taking its natural course. It could also be that you have an undersized expansion tank (a very common problem if retrofit).

If this is a recently installed all-copper, sweat-connection system, look for inadequate expansion loops. That can crack a joint or fitting

*just* enough for a tiny leak visible only under pressure.

There are just too many variables to diagnose a problem without additional information.

Lastly, Miracle-Shyte-Glyte-Leakstop is NOT what you want to install in any system, especially a high-efficiency copper-based (if that is what this is) system. It will greatly degrade the heat-exchange equations going and coming and is altogether a bad idea. Find the cause of the pressure drop and fix it.

Peter Wieck Wyncote, PA

Whoops. In that case, I gave bad advice. I'd assumed that this was like any other plumbing system and would withstand city water pressure.

M Kinsler

It happens. Few individuals understand radiant heat anymore. It is a wonderful system designed properly and can be very efficient as it puts heat where it does the most good. But, sadly, it does not support central AC, a major drawback these days.

Peter Wieck Wyncote, PA

m kinsler inscribed thus:

Actually, thinking about it, that is a good idea ! The system should be able to withstand 50 - 100 psi without too much stress. The soap water trick should work well.

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Best Regards:
                      Baron.

Agreed that 50 PSI is way too much, but I don't see a problem with pressurizing it. When I test automotive cooling systems I pump them up to about 3 PSI with a bicycle pump, I do this on top of the water already in there, at which point it will usually drip from the leaky part instead of coming out as invisible steam.

Do you know about Hydronic heating systems? Any domestic system that I know will blow (at least) several gaskets if pressurized to 50#, possibly more if done so 'dry'. I guess you could tie down or cap the TPR valve and take your chances, but the other potential is that many more joints might fail if it is a threaded iron system.

Keep in mind that older systems required pressure only enough to bring water to the highest point in the system, cold. Normal expansion would then increase the pressure under operating conditions with water at anything from ~140F to 180F (60C - 83C) depending on the type of system and radiator/heat-exchanger design. So, the system would be provided with an expansion-tank. Some were open and at the top of the system, some were gravity and at the bottom. Today, pre-pressurized bladder tanks are used such that they will maintain near-0 content cold but accept expansion without a significant increase in system pressure.

We run a system with a 12-meter rise at about 15 psi (1.03bar). When at operating temperature (140F/60C) pressure increases only to 18psi (1.24bar), not much considering it is a black-iron two-pipe system. Just for the sake of clarity, a "two-pipe" system means that each radiator is the same virtual distance from the boiler, and so each radiator heats up at the same rate and at the same time. It is easy to conceive: Draw two parallel lines, label one "supply and the other "return". The individual radiators cross from the one side to the other. Now, draw a line from the SUPPLY side on the right to a box. And from the RETURN SIDE on the left to the same box. Label the box "Boiler". You can see that the radiator closest on the supply side is furthest on the return side, and vice-versa. The one in the middle is equi-distant. That is how it works. Our TPR valve is set for 30psi/

200F. Some margin, but not a huge amount nor would we want it so.

Most modern installed systems are simple loops. The radiator closest to the supply heats first. The guy last in line gets short shrift.

Peter Wieck Wyncote, PA

snipped-for-privacy@aol.com inscribed thus:

Thankyou for your notes. I did say up front that I was not a plumber! However I do understand what you are saying and appreciate it. I can see why pressurising a system in the way described is not a good idea. I withdraw my comment unreservedly.

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Best Regards:
                      Baron.

As I have written before, hydronic systems are nearly a lost art in domestic applications. I have installed two in my time and repaired MANY, and I am perhaps the youngest person (at 55) that I know not a professional plumber or engineer that has any clue about their general operation. But I have lived in two houses with such systems, both over

100 years old, both retro-fitted from either stove/fireplace or coal- fired octopus systems to hydronics in the '30s. Self-defense has made me quite familiar with their vagaries.

Peter Wieck Wyncote, PA

Are you sure that water is not leaking through the pressure release valve? It sometimes evaporates and leaves no evidence. Can you temporarily connect a hose and a container to catch any water leaking from the pressure release valve pipe which exits outside the buliding.

Rudge.

Thank you all for your replies.

Firstly, in response to your first post Peter:

"How old is the system for one. Not the boiler, but the entire system."

Originally we had a gravity fed system fitted about 30 years ago with a cold water tank in the loft and a hot water storage tank below. This system was recently replaced by a Megaflo tank and Vaillant condensing combi boiler. As this is a pressurised system the cold water storage tanks were no longer requried. We replaced some of the radiators with newer ones and additional ones were added including a towel radiator.

a) What kind of system is this - One or Two pipe? I believe two pipe - Separate water and heating pipes. b) Copper or Iron? Copper c) Are there any direct copper-to-iron connections? I don't think so? d) What kind of expansion tank do you have? None e) And have you verified the pressure in it if it is a bladder tank, or have you drained it recently if it is a water tank? N/A f) Do you have automatic bleeder valves? If so what kind? Manual bleeder valves on the radiators. An automatic bleeder valve on the Megaflo tank I believe?

g) Do you have an automatic fill valve? Manual filling loop to pressurise the system h) One, two, three-or-more story application? Two storey i) How recent was the boiler installation? A few months j) How long has this been going on? SInce it was installed k) If this is a vintage system originally, was it sized for gravity or pump circulator? Gravity - pump l) And how big (how many radiators) is the system overall?

10 In general, how do you like this little boiler? As I understand it, it is a gas-fired, stainless steel, wall-hung condensing boiler? It is supposed to be a good reliable boiler. Hard to comment on performance as we have only had it installed for a few months.

"Rudge, in answer to your question: Are you sure that water is not leaking through the pressure release valve?

It sometimes evaporates and leaves no evidence. Can you temporarily connect a hose and a container to catch any water leaking from the pressure release valve pipe which exits outside the buliding.

Rudge."

I don't think any of the radiator bleeders are leaking. The only leak I spotted was on the towel radiator valve which was tightened by the plumber.

I have noticed a stream of water escaping from the flue while the boiler is operating which I find rather strange?

Thanks.

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M.Joshi

I have also seen the PRV fail. The spring weakens slightly. It holds the pressure when cold and topped up even to 3 bar when we tested it but weeps slightly in service so the pressure drops slowly over several days when in use.

HTH

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Mitch

terminal_crazy@sand-hill.freeserve.co.uk
www.sand-hill.freeserve.co.uk/terminal_crazy

A couple of things first:

a) Condensing boilers exhause either 'steam' or steam with a small stream of water. That is their nature and not of concern. The chemical reaction is 2CH4 + 3O2 = 2CO2 + 4H2O or, lots of water.

b) "Two-Pipe" system relates to how the radiators are fed. A loop- system puts the radiators on a loop such that the radiator nearest the boiler sees hot water first, then the next and the next until the entire system equalizes, excepting that the last radiator in the line is always coolest. A "Two-Pipe" system sets up parallel supply and return lines such that all the radiators "see" the boiler at the same distance. The first radiator on the supply side is the last on the return side, the last on the supply-side is first on the return side. This system heats all the radiators at the same rate simultaneously and is the most efficient except that it requires 50% more pipe and very careful planning/engineering as compared to a loop system.

c) I am gathering that your system provides domestic hot water as well as heating water, and so here in the US, we would call it a "summer/ winter hook-up". That is quite an elegant use of these boilers, about the only thing more efficient than such a system would be some of the tankless instant-hot water-systems.

But, cutting to the chase, somewhere, some how, there *must* be an expansion-tank. Your Megaflo tank is simply a heat-exchanger loop from the boiler to a domestic hot water storage tank, and most emphatically

*NOT* an expansion tank. The bleeder is for the domestic water side, not the central heat side.

If you do not have an expansion-tank within the system, may I gather that you have not yet used it for heat in the winter? Because when you do, you will absolutely blow off the TPR valve, which if not vented outside will be a hot, smelly mess on top of which you risk boiling out your system otherwise. And, this is absolutely the source of your pressure drop. The system is over-pressurizing each cycle and either venting through the valve slowly or at some hidden fitting.

Please check again for an expansion tank. With only ten radiators, it may be as small as a football (soccer ball, for the US) and hidden in some corner somewhere. If you have one, make sure that it is properly pressurized and/or properly drained (if from the old system). If it is a bladder-tank there will be a Schrader-valve on it that you may check with a tire pressure gauge and charge with a bicycle tire pump. For 2 stories, charge it to about 12psi... and MAKE SURE it holds at that pressure.

An all-copper system only 30 years old would not be gravity. Gravity systems use VERY fat pipe on the return side relative to the supply side and special valves such that expanding (freshly heated) water pushes through the valve causing flow. They are typically designed against standing-pilot systems with millivolt-pile thermostats run from electricity generated by the pilot through a thermocouple. These were designed for areas where mains power either did not exist or was unreliable. Very elegant, very simple. Not terribly efficient by modern standards.

Peter Wieck Wyncote, PA