Megaflo Pressure 0 Help

[dogcuddles]

Hoping for some help please

We have a megaflo system in the loft. It's fairly old but we (mostly! Know how to keep it ticking over!)

We know that bleeding radiators can cause the pressure to be lost from the system and we use the valves on the megaflo to get the pressure back up again.

Yesterday we bled the bathroom towel rail which had a LOT of air in it. Pressure had dropped to 0 so we went up to get it back to between 1-1.5 (which we had been told was correct).

In the evening the pressure again dropped to 0... and again overnight. This means neither hot water or heating will come on.

I'm unsure why this is now happening without us doing anything.

Any ideas as each time we need to fix it, it requires a trip up to the loft to recalibrate the pressure on the cylinder....

Any help gratefully appreciated!

You will need to top it up again. If there was loads of air in the radiator it suggests you might have a leak somewhere though?

where Is your gas boiler and which boiler is it?

You are getting confused as to what is the megaflo and what is your CH loop.

The megaflo is the hot water cylinder (big tank). This is pressurised by the mains water feed. You shouldn't need to repressurise it. Sometimes the air bubble in the top of the cylinder disappears and you have to restore it (often water will drip via the pressure release/tun dish if this is the case). You can see videos of how to do this on Youtube.

The CH loop is a pressurised water heating loop that runs inside the megaflo cylinder and through your radiators. In a pressurised system it has to be pressurised in order for the boiler to operate (normally at least 1.0 bar). If you have a pressurised system then normally there will be a gauge on the front of the boiler that reads the pressure, and a tap normally underneath the boiler that allows you to let more water into the system to pressurise it.

I assume this is what you did last night - turned on the tap and repressurised the system in order to get the boiler to work.

The problem is once you pressurise the system there is literally nowhere for the water to go. So if you repressurised it and it has now gone back to zero there is probably a leak somewhere in the CH loop. It could be an air leak or a water leak (systems sometimes can be water tight but not air tight). The fact that your towel radiator had a lot of air indicates this might be the case.

Thanks so much for your replies

I have a poorly child with me today but let me try and answer the questions.

My knowledge of plumbing and heating goes as far as turning a tap on and off and bleeding a radiator so I'm certain I'm not explaining the situation very well

I'll be back with more info

Ok, I'm going to try and explain the set up and what we did and really hope I make sense!

1. Megaflo did need venting as @GasPanic rightly asked as the overflow pipe was leaking. We followed the instructions to do this and get the air bubbles out. And have done this regularly since moving in with no issues

1. Our towel rail in the bathroom comes on with the hot water rather than the heating and is run oddly from the hot water pipes we figure (?) as it only comes on when the hot water is being heated up. This regularly needs bleeding as there is air in it

1. Whenever we bleed the towel radiator, the pressure in the megaflo (big cylinder in the loft) drops to 0 which means the hive switch goes nuts whirring as hot water won't come on.

1. To get the pressure back up to between 1 and 1.5 on the megaflo we have to turn two valves on the pipework. Usually this then resets and everything works perfectly

1. For some reason, this last time the pressure keeps dropping to 0 without us doing anything (I have checked I tightened the radiator value). We can get it back up again but each time requires us going into the loft

1. Through this whole process the boiler isn't touched. We have a Worcester standard 24kw boiler which is fairly new (6 years). This is on the ground floor

I'll enclose photos of the valve that shows pressure on the megaflo which is the one showing 0 (again, I might be misnaming it?)

Any help would be fantastic

First thing to check. Run the heating with the system pressurised at 1 to 1.5 bar. After 30 minutes or so check the pressure. Is it stable at 1.5-2 bar or has it gone past the red mark at 3 bar?

Thanks for the reply. Is there a reason you might foresee the pressure going up? We've not so far seen excessive pressure but I guess I don't know what that could look like

A sealed system such as yours will incorporate an expansion vessel. This vessel provides a cushion against the rise in system pressure that occurs you heat water for heating or hot water.

if it is faulty then it can creep above 3 bar. At this point the excess pressure is relieved through the valve with a red cap (attached to the gauge in your picture).

once the system cools back down you’ll find the pressure gone.

That dial is not measuring the pressure inside the megaflo cylinder. It's measuring the pressure in the central heating/hot water loop (the water that goes round the radiators and into the megaflo heat exchanger).

The megaflo cylinder is pressurised via mains water that goes in via that pipe that has the blue circle on it on the cylinder.

Your CH loop is normally a closed circuit at pressure that you can refill. That is what that braided flexible pipe and the two black taps are for - refilling the CH loop.

On my system you fill the CH loop via a tap close to the boiler and read the pressure in the CH loop off the boiler. I expect you have no cold water pipe near the boiler which is why they have put the fill tap for the CH loop and pressure gauge up here.

Your towel rail has been plumbed into the hot water side of the CH loop. Probably so that it always comes on when the hot water is on so you don't need to put the radiators on in order to warm up the towel rails. It's a feature rather than being odd :)

My guess is that there is a leak somewhere in your system, and the towel radiator is the highest point on the system, so it is where the air goes to when it replaces the water that is lost.

After you pressurised the system last night, did you turn on the radiators or the hot water at any time ?

Did you check to see whether you can see any leaks ? The problem is if you keep repressurising it and there is a leak, then obviously the water will keep coming out. The problem with this will be that the water in the loop is normally quite nasty and full of black gunk and inhibitor and if it leaks over your ceilings for example it will wreck them.

What 4naansjeremy says is also a possibility.

The expansion vessels normally have a rubber diaphram that wears out over time. So are a common part to fail.

I just wanted to come back to this thread to say a massive thanks for all of the responses.

@GasPanic I now understand my system and set up a lot more so thank you. I assumed as the dial was on the megaflo, that was what it was measuring.

@4naansjeremy seems to be right. The pressure crept up to 3 before the outlet pipe shot out some water (I guess to relieve the pressure?) and it went back down to 0.

So this pointed towards the expansion tank

Thanks to this advice, it meant I was able to ring my heating engineer already having diagnosed the problem and after he asked me to tap on the tank, it was clearly dense and full. He then bought a new tank on his way over and was able to resolve and replace without the usual faff of trying to work out the problem

So this thread definitely saved me £ in additional charges. Thank you.

That’s brilliant news!!