Pressure fluctuations - help!

jeremypearce · January 2011

I have an Ecotec Plus condensing boiler put in 2 years ago in a 1970s 4-bed detached with rad system and hot water.

At the last service the engineer said that the boiler had somehow put itself into almost idle mode and he reset it. Now the heating is great and all is good.. not

We woke up a week later and the pressure was zero - F22 error. I filled up to a couple of bar and all came on again. One radiator was stone cold but after 3/4 hour suddenly decided to come on - suspected a blockage that cleared itself...

In fact I didn't put that much water in and the pressure seemed to be rather high so I bled a bit out.

Anyway, all was well for a while but day by day the pressure when cold fell to almost zero again after about 3 days.

Funny thing is hot pressure is very high - almost 3 bar maybe - and stays that way throughout.

No sign of any rad leaks. There is a small warm patch in the shower room floor closeish to the rad down pipe, but the concrete surface is bone dry - may be nothing..

If it was a leak, where does the water come from to restore pressure when hot? I realise Boyle Law etc does increase pressure, but surely not by almost the entire scale?

Could all this be explained by gunge in the system? I have to confess to not having flushed the system before installing the new boiler. We do have a Magnaclean installed though and when I did bleed some water out it was clean.

Does this sorry tale make any sense to anyone out there?

Tim McElwain · January 2011

The EcoTek is made by Vaillant if I am

not mistaken. It sounds like you may have some frozen pipes or perhaps a pipe has let go.

There should be a pressure reducing valve on the city water feed to the boiler with perhaps a shut off ahead of it. The shutoff should be full open and the PRV should keep your pressure around 12 to 14 lbs at all times.

Tim McElwain · January 2011

Which Model EcoTek do

you have? I just looked up the boiler and according to the I & O manual it looks like they want you to fill the boiler with a hose and then close it up when it is pressurized. Do you have a city water line feeding your unit?

jeremypearce · January 2011

More details..

Thanks Tim..

The boiler is indeed a Vaillant Ecotec Plus 624.

The mains inlet feed is manual - just a hand lever valve. I think my engineer said it should have an outlet pie as well, but it doesn't. I can bleed pressure out by draining from downstairs rad.

I am in UK and although very cold frozen pipe not really likely in fact.

I have put a plastic bag on the PRV pipe sticking out of the wall outside (quite high up). It did spill about a teaspoon of water into the bag initially, although I thought it might be condensation - its very cold and damp outside. Nothing more overnight. I will keep an eye in it today.

Condensate pipe is plumbed into the back of the toilet. I took it out and had a look but no obvious drips there.

Pressure overnight fell but to quite low but again increased on heating coming on and is back in the high range as before just now.

Another pipe/rad inspection and a bit of listening to the radiators this morning came up with nothing again. Dry as a bone.

Appreciate your words of wisdom...

Jamie Hall · January 2011

I assume...

that there is an expansion tank in there somewhere? It sounds to me as though if there is, that it is water logged. It should have air in it, as well as water. If it doesn't, or if there isn't enough, what will happen is that as the water heats it tries to expand -- but it is almost incompressible so the pressure shoots way up. The expansion tank provides an air cushion, so that as the water expands from the heat the pressure doesn't change much.

Some older systems had instead just an open tank with a vent (and overflorw!) in the attic space. I don't think yours should be that old, but you never know. If the pipe leading to that open tank is frozen, that would do it too.

The cold pressure on your system should probably be around 1 bar (less if there's an open vented expansion tank in the attic), if it's a two storey detached, but it certainly shouldn't rise that much when it turns on and heats up.

Tim McElwain · January 2011

Jamie the Baxi Luna

has a built in expansion tank in the unit.

This job is in England and their piping and system requirements are very different from ours. They fill and pressurize a system with a hose then shot off the manual valve and leave a pressurized unit no back flow or PRV.

Jamie Hall · January 2011

Got that far...

that it was in England. Didn't realise that the Baxi Luna had a built in expansion tank -- shows you how little I know about hydronic heating! Thank you, Tim. But... I still say that the pressure fluctuation our man is seeing suggests that there is something amiss with the provision for expansion.

I have to admit that being obliged to fill the system with a hose may not be such a bad idea. Nothing like a complete disconnect to ensure no cross connection! In Edinburgh, Scotland, at least, the entire house is effectively disconnected from the mains -- there is a cistern in the attic which is filled automatically through a float valve which has an air gap. Not such a bad idea, really...

Pressure fluctuations - help!

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