Combi boiler pressure

[Alan ward]

Hi I suspect I have a leak in my central heating system. Have to refill it every 3 months when the pressure drops below the operating level. Replaced prv and pressure vessel as that was faulty but still having the same problems. More than will to pay someone to come round . I’m in Orpington Kent area . Can’t see a leak anywhere
Thanks alan

 

[Deleted member 120897]

Could be a microscopic leak, which are difficult to locate.

 

[exedon2]

As above micro leaks very difficult to find.
Rad valves worth checking particularly lock shields.
We never fit auto air vents when we can avoid it, always manual ones particularly when they cannot be easily seen.
Auto air vents have a habit of leaking.

 

[John.g]

You don't say what size boiler/expansion vessel. All expansion vessels should have a filling pressure ~ 0.3 to 0.5bar higher than the pre (initial) charge pressure. Some boilers clearly state what these pressures should be, others are a bit vague. The reason for the above is so as the expansion vessel has a small reserve of water when cold and avoids frequent top ups due to air venting etc. If you know/knew exactly the EV volume and the pre charge and filling pressures then you will know exactly how much you have "lost".
For example, a 10 litre EV with precharge/filling pressures of 1.0/1.3bar will have a water reserve of 1.3 litres but the same EV with precharge/filling pressures of 1.0/1.5bar will have a water reserve of 2.0 litres.
On the other hand if someone had only filled the EV to 1.0bar then there is no water reserve so very difficult to quantify your leak accurately. My only experiences with domestic expansion vessels is one relations oil fired system that has precharge/filling pressures of 1.0/1.5bar with a 12 litre EV, water reserve of 2.4 litres, (I installed it) and I am informed that it has "only" needed topping up once in > 2 years.

 

[ShaunCorbs]

Ideal combi chance are main hex split east way to test cut condense and put into a bucket overnight and leave boiler off / no demand

 

[Alan ward]

Could be a microscopic leak, which are difficult to locate.

Don’t I know it, what’s the solution

 

[Alan ward]

As above micro leaks very difficult to find.
Rad valves worth checking particularly lock shields.
We never fit auto air vents when we can avoid it, always manual ones particularly when they cannot be easily seen.
Auto air vents have a habit of leaking.

I only fitted them coz that’s what was recommended by the last engineer.

Ideal combi chance are main hex split east way to test cut condense and put into a bucket overnight and leave boiler off / no demand

Yes it’s an ideal boiler, I’ll get someone to do that. The problem got worse when we had a bad frost and the condenser pipe froze . I since lagged it and it hasn’t froze since . When it froze before it started pouring out the boiler .I wonder if that did any damage

 

[John.g]

What model do you have? And what are the cold and hot boiler pressures. Also when topping up does it take minutes rather than seconds to do so?

 

[Alan ward]

What model do you have? And what are the cold and hot boiler pressures. Also when topping up does it take minutes rather than seconds to do so?

 

[hometech]

with such a small drop in pressure I'd look at the radiators. Remember, you are lossing pressure, not water by volume, big difference

 

[Alan ward]

It’s a logic Combi 35. Not sure what you mean by the hot and cold pressures sorry .
If if goes down to the auto cut off pressure then it takes less 10 seconds to re pressure. Heating isn’t really my field of expertise I’m a fabricator

 

[Alan ward]

with such a small drop in pressure I'd look at the radiators. Remember, you are lossing pressure, not water by volume, big difference

That’s reassuring, there doesn’t appear to be any leaking around the valves . There’s the usual gunge where it’s resealed it self around the fitting on a couple of rads

 

[EvilDrPorkChop]

3 months isn't much, personally at that I wouldn't worry about it.

If it gets worse, then yeah it's something to think about.

 

[hometech]

3 months isn't much, personally at that I wouldn't worry about it.

If it gets worse, then yeah it's something to think about.

not good advice from an engineer is it..wait until its serious...like taking a car into the dealer and they say when the engine seizes we will fix the oil leak..

 

[EvilDrPorkChop]

not good advice from an engineer is it..wait until its serious...like taking a car into the dealer and they say when the engine seizes we will fix the oil leak..

Unlike you speaking from experience, a pressure drop over 3 months is very very minimal. On an old system you will get pressure loss, it's very rare that you have a system that won't loose pressure over 6/12 months.

My advice was, that if it gets any worse then it needs attention. Even if you were topping it up every 2 months it still wouldn't be a major leak.

 

[Alan ward]

3 months isn't much, personally at that I wouldn't worry about it.

If it gets worse, then yeah it's something to think about.

Yeah it’s not perfect but 0.5 of a bar isn’t a lot to

Unlike you speaking from experience, a pressure drop over 3 months is very very minimal. On an old system you will get pressure loss, it's very rare that you have a system that won't loose pressure over 6/12 months.

My advice was, that if it gets any worse then it needs attention. Even if you were topping it up every 2 months it still wouldn't be a major leak.

its probably something I’m gonna get looked at in the summer. I’ve just topped it up with a bit more inhibitor.
I just want someone to come sort it, I’m more that happy to pay someone to come do it . Cheers people

 

[John.g]

It’s a logic Combi 35. Not sure what you mean by the hot and cold pressures sorry .
If if goes down to the auto cut off pressure then it takes less 10 seconds to re pressure. Heating isn’t really my field of expertise I’m a fabricato

The pressure ("gauge") I'm referring to is the one you watch while topping it up. The cold pressure is the displayed pressure when the system is cold, say, before boiler morning start up, the hot pressure is the displayed pressure any time the system has heated up, like right now.

Your boiler has a 8 litre expansion vessel and will have a reserve volume of 1.0 litres of water if pre charged to 0.75bar and refilled to 1.0 bar.

What is the pressure when you top it up and what pressure do you top it up to?.

 

[Alan ward]

The pressure ("gauge") I'm referring to is the one you watch while topping it up. The cold pressure is the displayed pressure when the system is cold, say, before boiler morning start up, the hot pressure is the displayed pressure any time the system has heated up, like right now.

Your boiler has a 8 litre expansion vessel and will have a reserve volume of 1.0 litres of water if pre charged to 0.75bar and refilled to 1.0 bar.

What is the pressure when you top it up and what pressure do you top it up to?.

I normally top it up to just over 1 bar. When it’s on full pelt heating up it can go up to about 2.5 bar but normally sits around 2 bar when it’s up to temperature

 

[hometech]

Unlike you speaking from experience, a pressure drop over 3 months is very very minimal. On an old system you will get pressure loss, it's very rare that you have a system that won't loose pressure over 6/12 months.

My advice was, that if it gets any worse then it needs attention. Even if you were topping it up every 2 months it still wouldn't be a major leak.

It has a leak or it does not have a leak, this is not theoretical physics where the leak is a quark lol. Engineers address problems before they become bigger problems, it is often called preventative maintenance. You do it with boiler servicing every year so what makes this different? Is a little gas leak OK to leave ?

 

[John.g]

Assuming that you are topping it up from 0.5bar (to 1.0bar), you are losing up to 2.0 litres.

 

[Alan ward]

Assuming that you are topping it up from 0.5bar (to 1.0bar), you are losing up to 2.0 litres.

You would think you would see that amount of water some . Like a stain on the ceiling. All comes through the loft. How would you go about locating it . I’m at a loss . Was thinking of using one of the leak detection services but I don’t know much about them

 

[John.g]

IF you are topping up from 0.5bar, are you? then perhaps a bit more than normal. Why don't you carry out that suggested condensate pipe leakage test first, you can do this yourself relatively easily.

 

[hometech]

Assuming that you are topping it up from 0.5bar (to 1.0bar), you are losing up to 2.0 litres.

So 0.5bar is 2 l? How do you calculate that?

 

[Alan ward]

IF you are topping up from 0.5bar, are you? then perhaps a bit more than normal. Why don't you carry out that suggested condensate pipe leakage test first, you can do this yourself relatively easily.

 

[Alan ward]

Ok , can you tell me how to do that in steps please. I’ll try that next weekend
Thanks

 

[John.g]

The condensate test??
Will revert tomorrow, must go out now shortly.

What pressure is the boiler tripping out at??

 

[Alan ward]

The condensate test??
Will revert tomorrow, must go out now shortly.

What pressure is the boiler tripping out at??

Just below 0.5 I think . Have to check the book

 

[John.g]

So 0.5bar is 2 l? How do you calculate that?

A good question, I'm assuming that the precharge pressure is 0.5 bar, so a filling pressure of 1 bar gives a reserve of 2.0 litres, however, I did say losing up to 2 litres, obviously, if the precharge pressure is 0.75bar then loss is only 1.0 litre as the pressure will fall to the static head once the EV diaphragm is hard up against the water end, any further loss below 0.5bar would be far more worrying as you are then using the water from the upstairs rads as your reserve assuming EV downstairs.

 

[John.g]

Ok , can you tell me how to do that in steps please. I’ll try that next weekend
Thanks

As in post #5, you will have to identify the plastic condensate pipe and "break" it and measure any leakage but well after the boiler cools down, however I fear that it is like looking for a needle in a haystack at a leakage rate of say 1.5 litres/3 months = 0.69ml/hour or ~ 7ml in 10 hours.

You might be better off just now locating the boiler PRV (safety valve) waste pipe, it is generally a 1/2 ins copper pipe that might exit through a wall at the rear of the boiler and is turned inwards, when you do, tie a plastic bag around it and observe it for a few hours with boiler operating normally, this might just possibly be passing very slightly especially if the boiler pressure is reaching 2.5bar occasionally as you stated above. It is not shown in the above schematic but the condensate pipe is.

 

[Alan ward]

As in post #5, you will have to identify the plastic condensate pipe and "break" it and measure any leakage but well after the boiler cools down, however I fear that it is like looking for a needle in a haystack at a leakage rate of say 1.5 litres/3 months = 0.69ml/hour or ~ 7ml in 10 hours.
View attachment 73706
You might be better off just now locating the boiler PRV (safety valve) waste pipe, it is generally a 1/2 ins copper pipe that might exit through a wall at the rear of the boiler and is turned inwards, when you do, tie a plastic bag around it and observe it for a few hours with boiler operating normally, this might just possibly be passing very slightly especially if the boiler pressure is reaching 2.5bar occasionally as you stated above. It is not shown in the above schematic but the condensate pipe is.

As in post #5, you will have to identify the plastic condensate pipe and "break" it and measure any leakage but well after the boiler cools down, however I fear that it is like looking for a needle in a haystack at a leakage rate of say 1.5 litres/3 months = 0.69ml/hour or ~ 7ml in 10 hours.
View attachment 73706
You might be better off just now locating the boiler PRV (safety valve) waste pipe, it is generally a 1/2 ins copper pipe that might exit through a wall at the rear of the boiler and is turned inwards, when you do, tie a plastic bag around it and observe it for a few hours with boiler operating normally, this might just possibly be passing very slightly especially if the boiler pressure is reaching 2.5bar occasionally as you stated above. It is not shown in the above schematic but the condensate pipe is.

Ok

As in post #5, you will have to identify the plastic condensate pipe and "break" it and measure any leakage but well after the boiler cools down, however I fear that it is like looking for a needle in a haystack at a leakage rate of say 1.5 litres/3 months = 0.69ml/hour or ~ 7ml in 10 hours.
View attachment 73706
You might be better off just now locating the boiler PRV (safety valve) waste pipe, it is generally a 1/2 ins copper pipe that might exit through a wall at the rear of the boiler and is turned inwards, when you do, tie a plastic bag around it and observe it for a few hours with boiler operating normally, this might just possibly be passing very slightly especially if the boiler pressure is reaching 2.5bar occasionally as you stated above. It is not shown in the above schematic but the condensate pipe is.

As in post #5, you will have to identify the plastic condensate pipe and "break" it and measure any leakage but well after the boiler cools down, however I fear that it is like looking for a needle in a haystack at a leakage rate of say 1.5 litres/3 months = 0.69ml/hour or ~ 7ml in 10 hours.
View attachment 73706
You might be better off just now locating the boiler PRV (safety valve) waste pipe, it is generally a 1/2 ins copper pipe that might exit through a wall at the rear of the boiler and is turned inwards, when you do, tie a plastic bag around it and observe it for a few hours with boiler operating normally, this might just possibly be passing very slightly especially if the boiler pressure is reaching 2.5bar occasionally as you stated above. It is not shown in the above schematic but the condensate pipe is.

Thanks I will do the thing with the condenser pipe. I’m guessing I can just pull it out the boiler and put a bucket underneath.

 

[Alan ward]

Someone else has thrown a spanner in the works . Said the pressure vessel may not be able to handle the size of the new column rads we put it . To be fair with one of them is massive. Might be nothing and just information overload

 

[John.g]

Alan, that's a possibility all right but if so then the boiler PRV will lift and discharge water at 3bar pressure, you did say you have/had seen it at 2.5bar so you should do what I suggested above in my last post, for info a 8 litre EV will accomodate a system volume of 180 litres (quite alot) before reaching 2.8bar from pre/filling pressures of 0.75/1.0bar.

If the PRV has lifted a few times it could now be dribbling even at normal hot pressures of 2/2.5bar.