Vaillant Ecotec Pressure Too High

[No More Heroes]

I have a Vaillant Ecotec plus 637 boiler. The pressure is very high and pegged to the right - water is dripping out of the outside overflow through the Pressure Release Valve. An engineer has replaced the expansion vessel and checked the filling loop.

The pressure gauge is still pegged. (Note: The boiler has shown no error code at any time).

Its now been suggested that the problem is with the 20 year old Ariston WRc-NSF unvented hot water cylinder, which is not covered by my maintenance plan and will be expensive. I can't see anything obvious, like water coming out through the tundish, but no idea what to look for.

Does that all sound right?

 

[ShaunCorbs]

Have you disconnected the filling loop and drained the extra pressure?

Also does it start to rise immediately/ can’t drop the pressure ?

 

[No More Heroes]

Yes. Starts to rise immediately

 

[ShaunCorbs]

Do you have an isolation valve on the cylinder?

 

[No More Heroes]

Let me take that back - I thought the pressure rose straight away when the engineer was here.

I've just bled a radiator (about 1/2 washing up bowl) and the pressure gauge on the boiler has gone down to midway on green. The heating is currently off.

 

[ShaunCorbs]

Leave the heating off and hot water and monitor over the next 2 hours

 

[No More Heroes]

Roger that - Will do! So, if it goes up, does that mean that there is a problem with the cylinder? Or could it be something else?

 

[ShaunCorbs]

Let’s see what happens first

 

[No More Heroes]

Two hours later and the dial hasn't moved!

 

[ShaunCorbs]

You haven’t touched any valves eg turned off if so Expansion issue likely then so hose or port blocked call them back out as it’s not fixed

 

[No More Heroes]

2.5 hours more and the dial still hasn't moved. No water coming out the outside overflow for the last few hours either. Water heating has been on. Will try the central heating later to see what happens then

 

[John.g]

Even with everything OK it should move up a little on any increase in temperature.

 

[No More Heroes]

Had the heating on for a bit last night and it stayed in the green. Have been keeping an eye on it today and its still in the green. There has been no leaking from the overflow since I bled the radiator - For the couple of days before that, the leak was less than before the engineer replaced the expansion vessel.

 

[No More Heroes]

Aaaargh! After a few days I've noticed that the pressure dial has moved up from middle of the green into the edge of the red. I've bled a radiator again to get the pressure back down.

What should I do for a permanent fix?

 

[John.g]

These were suggested previously, disconnect the filling line see if it's leaking past, if not shut cold water to cylinder and open tap to reduce pressure below boiler pressure , see what happens.

 

[No More Heroes]

First one has been done twice. I don't know how to do the second bit.

 

[John.g]

It might look something a bit like this, just shut the "Cold Main" valve and open a hot tap to depressurize the HW cylinder.

 

[No More Heroes]

Is the cold water tap the one at the top right of this picture?

(The engineer who came to look at my system said the cylinder needed replacing because there was something broken inside it.)

 

[John.g]

Look at the tee in the expansion vessel and see if one of the pipes off it goes down into the bottom of the cylinder and also check that the downward horizontal pipe to the right of the valve comes up from the ground, if so then this is the cold water isolating valve.

 

[EvilDrPorkChop]

Is the cold water tap the one at the top right of this picture?

(The engineer who came to look at my system said the cylinder needed replacing because there was something broken inside it.)

View attachment 62834

The Anode will have failed, so he's right it'll need replacing. It's more than likely the cause of your pressure increase too, there's probably a pin hole in the coil causing fresh water to leak back into the CH system.

As other's have said you can isolate the cylinder and let off the pressure at a Hot tap, and monitor the pressure on the CH side.

 

[No More Heroes]

Closed the tap (on the top right of the picture) and then turned on a hot water tap. Hot water came out for a few seconds and then stopped. Left it for a few minutes like that. Didn't notice any change on the dial on the boiler.

 

[John.g]

If the cylinder coil is (pin) holed, then, depending on the hole size, the boiler pressure should actually start falling if you leave the cylinder depressurized and the hot tap opened long enough, this crack in the coil (if it exists) may not show up until the coil heats up so would suggest leaving the cylinder depressurized maybe overnight with the hot tap opened, the boiler pressure certainly shouldn't rise excessively then, a few minutes test is pretty useless IMO.

 

[No More Heroes]

Ah! Got it. I'll give it a go overnight tonight. Thank you.

 

[No More Heroes]

Now quoted £1900 to replace existing cylinder (Ariston) with a 'Telford Tempest 500 Litre Stainless Steel Indirect Unvented Cylinder'. Is that about right and a good choice?