Too much pressure.......

[Alastair]

Hi,

This is going to take ages to explain but here goes.....

I have a pressurised CH system with a Hatrea Sadre pressure thingy in the airing cupboard as the hotwater tank. The house is quite sprawling so there are some long runs of pipe around the house. The general problem I have is this, you have to leave the pressure of the system around 1BAR on the dial on the boiler. Basically after time as the house heats up, the pressure builds up until it hits 3.5BAR and then the pressure release kicks in and water comes out of the pressure release pipe. When everything is cold, the pressure has dropped to below .5BAR and needs topping up, otherwise the pump makes a real racket until it has been running for a while and the pressure gets back up.

So I assume that the pressure gets higher over time as all of the rad stats start to close as the rooms get to tempurature. There are 4 rads in the loos/bathrooms that have no stats, and I have checked they are all fully open. Also we have a kitchen with a conservatory which always is never as hot as the rest so these are always on, basically a total of 7 rads that are still "open" and I still have over 3.5BAR of pressure.

I can only assume this is not right, but don't know where to start trouble shooting. Anyone got any good ideas/pointers.

Thanks in advance

Alastair

[Neil Jones]

There should be an expansion vessel somewhere on your system, which is designed to take up some of the expansion the system water undergoes as it is heated. It seems on first glance that either your expansion vessel has failed or, given you say the house is quite big, it might not be big enough for the system, meaning it should be replaced or augmented.

HTH

Neil

[John Rumm]

Sounds like your expansion bottle has failed / or needs re-inflating, or is not large enough for the volume of water in the system. If it used to work ok, then then former sounds more likely.

Have a look at Ed Sirett's FAQ on sealed CH systems:-

[Set Square]

Presumably the "Hatrea Sadre pressure thingy" is an expansion vessel which is designed to take care of the volume increase when the water gets hot without excessive pressure building up. There will be a relief valve which lets water out if the pressure exceeds 3 bar.

Under normal circumstances, if the system is pressurised to 1 bar when cold, it shouldn't exceed 2 bar when hot. Since yours is going higher than this, either:

• the expansion vessel is duff, or

• it is not big enough for your system

Has it ever worked properly? If so, the vessel may just need re-charging. It has a diaphragm inside with compressed air (or maybe nitrogen?) on one side and water on the other. Is there a valve on the side to pump it up with air? Do you have an installation manual for it - which would tell you what air pressure to use?

[OldScrawn]

existing 7l one is buried in the guts and you can't even test it without a fairly major dismantle I am going for 12 l. Not particularly expensive, about £14 plus vat from bes, and not a difficult job provided you can get to your CH return at a convenient point.

[Alastair]

Hi,

Firstly thanks all for the replies, very helpful. I think I am getting down to the bottom of this. Just for info:

a) I have never been happy with the system, I have always ended up having to tinker with it b) The house is only four years old, but I bought it off someone who got relocated and never lived in it, so essentially it was new, but the builder would not entertain "snagging"

We have a Heatre Sadia Megaflow CF in the airing cupboard

and I always assumed that this held the air gap for the pressure gain in the central heating. However now I am not so sure, I think that the air gap in this unit is only to retain pressure in the hot water system, am I correct?

Secondly assuming this is so, I have no expansion vessel in the central heating system at all. If the house was built 5 years ago, would this have complied with building regulations?

Taking it further, I think a lot of my problems started when I started to get really serious about bleeding the rads, and there was quite a bit of air in a lot of them, hence I would have had some expansion capabilities there, am I on the right track?

Just as a thought, if the system was installed 5 years ago, not to building regulations do I have any recourse to the builder?

Thanks again

Alastair

>

[Andrew Gabriel]

Think so.

Are you sure it isn't inside the boiler casing? If the pressure guage is on the boiler, then it likely is. What boiler model is it?

I don't think building regulations cover this.

[Alastair]

Andrew,

I have a Vokera Minute 28se, it does have a gauge on, so maybe it does?

Cheers

Alastair

[Set Square]

The thing in the airing cupboard sounds like a mains pressure hot water system - and nothing directly to do with the primary heating circuit.

If you have a pressurised central heating circuit you *must* have an expansion vessel - it is virtually inconceivable that it could have been installed without. It seems likely that you have a "system" boiler - with the filling loop, expansion vessel and pressure gauge all integrated within a single case.

The diagnosis is the same as before though - the expansion vessel has insufficient capacity, either because it wasn't big enough to start with or because it has developed a fault.

You need to find it, see what pressure it has on the air side, whether water has entered the air side, and act accordingly. It seems to me that there are

3 possibilities:

1. If water comes out of the Schrader valve, the diaphragm is split and the vessel will have to be replaced.
2. If no water comes out, but the air pressure in it is very low, pumping it up to 1 bar may be all you need to do. [That rather begs the question as to why it lost its pressure, so the problem may recur]
3. If the diaphragm is ok, and the charge pressure is ok, the vessel simply isn't big enough. You will need to install a bigger one elsewhere in the system. You can leave the existing one where it is - there's no harm in having more expansion capacity than you need.

[John Rumm]

According to their web site, it has a 10L expansion chamber built in.

could not find a service manual there to get any details on the chamber (and whether it can be recharged). Perhaps you should give them a call and ask? Tel: [phone]

If it looks like its going to be expensive to fix in the boiler, you could simply add another expansion chamber somewhere else in the system since they are pretty cheap.

[Alastair]

Hi,

Hmmmmm, the expansion vessel is indeed behind the heat exchange in the boiler and has zero pressure, I have pumped it up to 1BAR (after opening the system), and will see what happens. However I suspect the diphragm has gone, hence assuming it has, it must be easier to install a new vessel in the airing cupboard rather than replace the one in the boiler?

Cheers

Alastair

[John Laird]

If the diaphragm has failed, I would have expected to have seen water exiting the valve as you fitted the pump hose to it. If instead you spent a little while pumping against air, it is probably ok. There's only three places the vessel can leak air - into the water, out a seam, or past the valve cap. Knowing how crap those car-style valves(*) are, I'd put my money there.

Incidentally, if it's a Vokera, the pressure should be 1 bar plus the static head at the boiler, to maintain 1 bar throughout the system. 1 bar = 32 feet. But you're probably only slightly under that, so don't panic. The pump adds another bit.

(*) What complete numpty decided these were good for just about every bike now ? I'm forever pumping up tyres for me and my kids.

[Set Square]

It *may* just have lost its air - possibly through the valve. Is there an air-tight metal screw cap on the valve, which has to be removed to blow it up? If not, you may be able to fit one. [Hopefully, the valve is threaded and the same as used on car tyres].

If the vessel really *has* failed, then best to abandon it and fit a new one elsewhere. You'll need to make sure though that the failed one isn't leaking water to the outside world.

[IMM]

On the return as near to the boiler as possible with no motorised valves between.

[Alastair]

Well so far so good, system *seems* to be functioning correctly. It doesn't have an airtight metal screw cap, just one exactly like on my cars. So I will monitor it and see what happens.

thanks

Alastair