My boiler keeps dropping pressure in the unvented system set up. The boiler brand is Main (I know it is not the best).
I recently had the external compressor replaced, but this has not fixed the issue. The 'expert' told me that I would have to keep topping up the boiler pressure whenever it drops. This is does not seem normal? Also, there is noise when taps a opened and the water pressure has dropped around the house. This has improved a little once the compressor vessel was replaced.
Multiple sites seem to suggest there may be a leak in the system. I came across this as a DIY fix (fernox f4 express leak sealer).
Would appreciate advice from anyone in the know as to what the issue could potentially be.
I'll probably get flamed for this, but my advice would be not to tamper with any gas boiler, and get someone in who knows what they are doing rather than listen to spurious advice on the internet. It may be cheaper in the long run and almost certainly safer. https://www.mainheating.co.uk/support/repairs
Started out with nothing. Still have most of it left.
Agree, it's best for a professional to look at the issue.
The guy who repaired it was a boiler engineer from a local company that has been in business for almost 40 years!
I was having problems a few years back with a Logic. The pressure would collapse within 24 hours. I got one clown in who claimed my radiators must be leaking. I eventually got in touch with Logic and paid for them to come out. The guy opened it and immediately pointed to about 5 components that needed replacing. He could tell by the colour of the metal without even testing them. He replaced the parts with new and all sorted, no pressure drop in the last two years.
Don’t mess around, contact the manufacturer.
There are multiple places for a leak I guess, mine was a pressure relief valve they went to a overflow that wasn’t sealing back down after opening.
Cheers..
Jase
Is this a combi boiler?Originally Posted by PS
Do you mean "Accumulator"? I will assume that it is a traditional pumped system with CH and HW loops, with Cold water header tank pressurising the HW tank.
First thing is to ascertain if the pressure is actual water loss or accumulator pre-charge air loss.
Unfortunately to check for accumulator precharge you need to vent the water pressure (just until pressure drops away, don't drain the system), then put a gauge on the air schrader valve. I think precharge should be something like 1.0bar but you are checking for almost complete loss here (but record what pressure you get). You can get a feel for air in the accumulator by how the pressure increases when you recharge the water side, but that takes a bit of 'experience' to know what re-pressurising an already 'solid' system 'feels' like.
Once you establish that the air pressure is still present - you can re-charge the water side to the correct pressure range on the gauge.
There may be a loss of air accross the diaphragm of the accumulator - which is getting vented from the water side via an auto vent valve (if fitted) - that would show as an overall loss of system pressure.
There may be a relief or vent valve in the system which has lifted and has not reseated fully - do you know where any auto-vent valves are? (might be one in airing cupboard). A leak from an auto-vent valve may evaporate mostly as it runs down a hot pipe, so might not show up on ceilings or floors. These auto vent valves are principally used for commissioning the system and should really be valved-out once commissioned. they are usually fitted with 1/4-turn valves upstream of them to allow this. Many builders don't bother isolating them after though.
Every time you recharge with a little raw water you are dilluting the inhibitor in the system so bear in mind that you may need to add some once you sort out the issue.
If it isn't any of the above - it is either:
Leak in pipework (check around all floor penetrations in case a vacuum cleaner etc has knocked one of the pipes up into the radiator) - but a leak could be under the floor too.
Leak across boiler heat exchanger. you might see this in the flue if it is horizontal and the boiler is cold/off
Leak across HW tank coil - but only if CH system pressure is greater than tank head pressure
Leak from a radiator/towel rail (due to corrosion from within) - should be noticible.
Some of the areas above can be checked by you, but if nothing is obviouus, you will probably have to get someone in - to go through the system. Ideally a Corgi Heating 'Engineer' with some decent recommendations.
Try and avoid using leak-sealer, it can cause more problems than it fixes.
Not sure why your 'expert' replaced a faulty accumulator (if that is what you refer to), and went on to say you would need to keep topping up the system. Sounds like he simply replaced "something", charged you for the work - without actually addressing the issue. Was he just a "plumber"?
That is my take on it, at least.
Same on mine, I also had a pressure relief vessel that had lost its air, meaning there was nowhere for the water to go as it pressurized, again it vented out through the pressure relief valve. The water is either leaking or expanding out of the pressure relief valve, its sealed so it has to go somewhere.
If the boiler pressure (system pressure) is say 1.0b cold (after sitting overnight) - what pressure does it increase to when you heat up the hot water or the central heating?
In a system where the accumulator diaphram has split or the precharge has gone - the water pressure will increase a lot on heating up, and possibly may even lift the relief valve(s).
Have the basics been checked? Boiler expansion vessel pressure, PRV, has the boiler been opened for an internal inspection of water carrying parts, Has the cold water expansion valve been checked, along with the combination valve?
Lots of things it could be but if it’s a persistent leak on a pipe or radiator / valve, you would normally see that.
This is very common and often the root cause of why a PRV is leaking.
He replaced the expansion vessel looks like this: https://www.bes.co.uk/expansion-vess...-litres-21194/
Yeah - that is what I assumed. Might save a lot of investigation if there is a quarter-turn valve between the accumulator and the system.
Main Heating uses Baxi technicians for repair services - https://www.mainheating.co.uk/support/repairs
Boiler losing pressure? Causes of low boiler pressure & how to fix them
Worst case scenario is the primary heat exchanger is leaking. We had this with our WB boiler but thankfully it was replaced for the cost of a call out charge only, otherwise it is normally more economical to replace the boiler.
You definitely don’t want to have to keep topping up the pressure as that will cause corrosion unless you are also regularly adding inhibitor.
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Any the wiser OP?
Started out with nothing. Still have most of it left.
Thank you for the replies.
Will give Baxi a call to arrange for their technicians to have a look.
I had a similar problem in my first flat with a slightly crappy Ariston boiler. To his credit my usual local heating engineer had a look and pretty much immediately said “I’m not sure - you should contact Ariston as I can start replacing parts but I’m not sure this will fix the problem”
Lo and behold an Ariston specialist immediately diagnosed a common problem with that particular boiler within two minutes and fixed it for a hundred quid.
So I’m firmly in the “contact the manufacturer” camp with stuff like this. Good luck!
But if it is a ‘system’ problem rather than a ‘boiler’ problem - you really need to do some preliminary work to save 2 invoices.
Fair enough - I only have a very basic understanding of heating systems. Your post is considerably more useful!
Been having a similar issue during the winter. Our boiler is a system boiler and operates on the basis of heating our hot water in a large sealed tank, which has a acctuator valve that opens and closes as the timer and thermostat confirm when the water is at temp.
There is then a further 'system / loop' that is controlled by an acctuator and signal from the room controls and timer.
During the winter the pressure was dropping after a few days. Since March the heating has been off and not once had to top it up, which, in my mind suggests I have a leak in the system and not a fault in the boiler...... wish me look finding it!
The joys of home ownership
Paul
Sounds like the expansion vessel in the boiler needs repressurising, with a bit of luck it should be a simple fix.
If it was a leak in the system the pressure would still drop.
If the overflow vent pipe tip gets cold enough to freeze open slightly, this would cause a pressure drop.
Cheers..
Jase
Probably your system has gone ‘solid’ after losing all or most of the air from the accumulator.
Heats up - lifts relief valve, loses a few cl of water, and when it cools back down overnight - the pressure plummets.
while it is off just now - collapse the water pressure and stick a gauge on the accumulator. Pump it up to about 2/3 of the normal system pressure and see if it goes down overnight. Put some soapy water on the Schrader valve to see if it is leaking, also.
If accumulator pressure stays up - repressurise the water side to normal pressure and record that pressure.
That could/should sort it.
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