Megaflow Problem

15 Feb 2009
Reaction score
United Kingdom

Hope someone can help. My Heatrae Sandia Megaflow Cylinder has developed a bit of a problem. The pressure gauge is showing max pressure and the cylinder makes a dull thumping noise every 10/20 seconds.

The problem began a few weeks ago. To start with, heating the water would cause the pressure to go to max. Flushing a toilet would bring the needle back to normal but would then slowly rise back up to max. If I used all the hot water in the cylinder, the needle would stay in a normal position but when the hot water came on again in the morning the pressure gauge jumped to max again.

Now, not even using all the hot water keeps the needle down.

The cylinder is about 9 years old and is model CL170.

I am about to get a plumber in but was wondering if anyone has any advice about what to expect; has my Megaflow bitten the dust?
Sponsored Links
Are you sure you have a pressure guage on the megaflo?

These do not usually have a guage as it is only the cold mains into it and hot taps out.

I suspect you may be referring to the pressure guage on the sealed system side, connected to the boiler etc.

If this is the case check the filling loop is fully closed and if it is check FAQ's on how to check the expansion vessel on the boiler or heating system, the red one.
I am sure the Megaflow itself is fine but it sounds as if you have a problem with the pressure reducing valve and the expansion bubble. You can reform the bubble by following the instructions on the side of the cylinder.

As these, if wrongly fitted or adjusted, can explode and bring down a house its important not to just call "a plumber".

Anyone working on these must have obtained the relevant Certificate.

Sponsored Links
All I can think is that the pressure reducing valve has failed, so letting in the full mains water pressure to the cylinder.
Thanks mate. I'm assuming the pressure reducing valve is the black thing above the gauge?

Until I get it fixed am I in danger?
Well yes and no - you are in danger if the two safety valves fail as well, but even if they work why risk it - get somebody out next week.

With a G3 certificate.

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