Does the pressure rise when the water heats up? if so its because the water is expanding
Sudden pressure loss from unvented system
- Thread starter golightlygl
- Start date
Does the pressure rise when the water heats up? if so its because the water is expanding
@newgasinstaller Yes, the pressure rises from 1.0 to 1.6 when the boiler is heating
@simond: We have a separate break tank and pump pushing 3b cold supply into the loft so that isn't the problem. Curious, eh? Unfortunately, the installer specified the Quinta Pro, no choice by me.
I agree that a leak seems the most obvious explanation but wouldn't we expect that a leak that can cause a drop from 1.0 to 0.4b would be very, very visible?
Can you explain one other thing: the Megaflo has, I understand, a diaphragm and expansion gap built in to it. So what is the purpose of the other red expansion vessel? It is on the primary circuit so does that mean it is just coping with the expansion of water in that circuit ignoring the hot water in the tank.
@simond: We have a separate break tank and pump pushing 3b cold supply into the loft so that isn't the problem. Curious, eh? Unfortunately, the installer specified the Quinta Pro, no choice by me.
I agree that a leak seems the most obvious explanation but wouldn't we expect that a leak that can cause a drop from 1.0 to 0.4b would be very, very visible?
Can you explain one other thing: the Megaflo has, I understand, a diaphragm and expansion gap built in to it. So what is the purpose of the other red expansion vessel? It is on the primary circuit so does that mean it is just coping with the expansion of water in that circuit ignoring the hot water in the tank.
The amount of water lost will depend on the system volume in terms of pressure drop. If you have low water content rads (eg: Copper finned or Aluminium) then a modest water loss could drop the pressure.
Worth mentioning that if you let air out of a rad, or it escapes out of an air vent this will be shown as a loss of pressure.
The red expansion vessel has nothing to do with the Megaflo. It contains a rubber bag to separate the air (or nitrogen ideally) that gets compressed when the rads warm up by the water expanding. Similarly, when the water cools and shrinks the bag returns to the normal volume.
The Megoflo has a trapped bubble of air which does the same thing but for the stored hot water only. Heatrae Sadia patented a floating baffle notion that is meant to permanently keep the air and water separate. It is wholly useless at this, consequently, after a period of time, the air gap gets eroded by the water removing it. Then the expansion relief valves trigger and you have a leak.
A big improvement to the flawed Megaflo design was introduced about 4 yrs ago. It is an A4 sized label they stick to the side telling you that it WILL leak and how to replenish the air gap. Now that is progress. If you are very lucky you won't need to replace the T&P valve when this has happened.
It is shame that their marketing guff doesn't mention the fact that the patent is bunkum because the floating baffle doesn't work.
Worth mentioning that if you let air out of a rad, or it escapes out of an air vent this will be shown as a loss of pressure.
The red expansion vessel has nothing to do with the Megaflo. It contains a rubber bag to separate the air (or nitrogen ideally) that gets compressed when the rads warm up by the water expanding. Similarly, when the water cools and shrinks the bag returns to the normal volume.
The Megoflo has a trapped bubble of air which does the same thing but for the stored hot water only. Heatrae Sadia patented a floating baffle notion that is meant to permanently keep the air and water separate. It is wholly useless at this, consequently, after a period of time, the air gap gets eroded by the water removing it. Then the expansion relief valves trigger and you have a leak.
A big improvement to the flawed Megaflo design was introduced about 4 yrs ago. It is an A4 sized label they stick to the side telling you that it WILL leak and how to replenish the air gap. Now that is progress. If you are very lucky you won't need to replace the T&P valve when this has happened.
It is shame that their marketing guff doesn't mention the fact that the patent is bunkum because the floating baffle doesn't work.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local