Pressure Loss (new EV, PRV and dosed with F4)

[Elraoak]

Have a large CH system, not sure the volume but a mix of column radiators and UFH means it's probably 250L or more. Runs on a Vaillant Ecotec 630 that's been OK for 7 years, but recently started losing pressure (needs topping up weekly).

Had a new EV (old one was full of water apparently). After that, I had drips from the purge pipe when pressure < 3 bar and so had a new PRV and it appeared to have stopped dripping.

Still losing pressure, so had 2 x Fernox F4 express added and whacked the system on to circulate it and pressure jumped to 3.6 (had added 800ml of fluid!). PRV did it's job, but I noticed that the PRV pipe was now leaking from the bottom of the boiler (think plumber hasn't fitted the pipe correctly after changing the PRV)!

None of this seems to be working. Nothing else has changed in the last year and the problem has only been around for the last few months.

What should I try next?

 

[SJB060685]

You need to get your engineer back to fix that drip first off.
Next if you cannot see any signs of leaks throughout the property have your engineer consider/check to see if the primary hex has failed. If so you would notice a constant drip from the condensing discharge while the burner is not firing.

 

[Elraoak]

You need to get your engineer back to fix that drip first off.
Next if you cannot see any signs of leaks throughout the property have your engineer consider/check to see if the primary hex has failed. If so you would notice a constant drip from the condensing discharge while the burner is not firing.

Trying to get them back, unfortunately no answer on any of the three phone numbers yesterday and no reply on email yet.

Am wondering also if the new EV wasn't pressurised properly. Have seen some for sale where the sticker says precharged to 0.75BAR.

If I understand it correctly, that would mean that when the system was filled to 1.5BAR then it would already be filling the EV? The EV should have been charged to 1.5?

Might explain why the pressure gets so high when running (which could potentially cause loss if it goes over 3 BAR early in the morning when all the heating zones are on).

No visible leaks anywhere (boiler was serviced when the EV was installed 22nd Feb). We put the F4 in just in case there were some micro leaks somewhere under the floor etc.

Condensation runs though a hard pipe into an internal drain, so no way to see a drip but I do hear a gurgle every now and then. Will mention heat exchanger to the plumber if I ever get hold of him!

 

[SJB060685]

The vessel is usually charged to .2 bar under system static pressure. If the vessel is to small in capacity or the charge is incorrectly set then the PRV will lift.
I’d have someone check it over. When charging a vessel it needs to be done when there’s no water acting on the diaphragm, ie drop some water out of the system first. If you don’t do this then you will have a false reading. If the original engineer returns and doesn’t do/know that then I wouldn’t have them back again.

 

[Elraoak]

The vessel is usually charged to .2 bar under system static pressure. If the vessel is to small in capacity or the charge is incorrectly set then the PRV will lift.
I’d have someone check it over. When charging a vessel it needs to be done when there’s no water acting on the diaphragm, ie drop some water out of the system first. If you don’t do this then you will have a false reading. If the original engineer returns and doesn’t do/know that then I wouldn’t have them back again.

.2? Did you mean 1.2?

They have to come back to fix the leak, so will get them to drain it down enough to drop pressure and check the charge in the EV.

It's only because I saw a sticker on one saying it came pre charged to 0.75 (and I didn't see him use any form of pump) that's made me wonder.

 

[SJB060685]

They all come pre charged. The engineer then has to adjust to suit system pressure, volume, flow temperatures and height of building etc.

 

[John.g]

If the engineer knew you have a 250 litre system then a external EV should be installed as gas boilers by their very nature have mean and lean EVs, your's is, I think 10 Litres, you will just about get away with it if the EV has pre and filling pressures of 0.75/1.0bar resulting in a final pressure of 2.72bar, pre/filling pressures of 0.75/1.5bar will result in the PRV lifting at 3baras the final pressure will, theoretically, be 4.93bar.

If you are installing a external EV then suggest 18 litre as you wont have to then replace the internal one if it fails and any plumber can replace it (external).

 

[Elraoak]

If the engineer knew you have a 250 litre system then a external EV should be installed as gas boilers by their very nature have mean and lean EVs, your's is, I think 10 Litres, you will just about get away with it if the EV has pre and filling pressures of 0.75/1.0bar resulting in a final pressure of 2.72bar, pre/filling pressures of 0.75/1.5bar will result in the PRV lifting at 3baras the final pressure will, theoretically, be 4.93bar.

If you are installing a external EV then suggest 18 litre as you wont have to then replace the internal one if it fails and any plumber can replace it (external).

Hi

The system wasn't as big when the boiler was installed, but over the years we have swapped out radiators for the three-column style ones, which hold a lot more water (some of them are ~20L each). So we could easily have added 50-100L to the system. This was all done by the same plumber - who never queried whether the boiler setup would work with the increased volume.

The last of the bigger radiators were installed in March last year and I don't remember problems until late last year (hard to remember - I just routinely started topping up the system once a week if it looked like it needed it). However they were installed towards the end of the colder months when the boiler was doing the most work (radiators are in three zones, so they aren't all always on), so it is possible the problems are linked back to having added those extra radiators.

Am afraid you have lost me with the pre and filling pressures. I assume "pre" is the pressure before it is installed, which is 0.75 from the factory according to the sticker (EV is 10L - yes); but not sure what you mean by filling pressure? Do you mean the pressure it is filled to when the system is "cold"? We do see 2.7-2.8 when running at 75C flow with the burner on full whack.

Presumably, the PRV will release any excess and bring it down to whatever volume of water if can handle at full whack; my problem seems to be that when the temp drops in the middle of the night, the pressure drops down below 0.8 and the boiler cuts out. usually, just a small blast from the filling loop is enough to get it back up and running - but that is not sustainable!

 

[John.g]

Correct, the pre charge pressure is the EV air/nitrogen pressure before installation but should always, without exception, be checked/corrected with a pump/pressure gauge. The filling pressure is the pressure that the system is pressurized to while cold by opening the filling valve. The filling pressure should always be 0.5 to 1bar > the precharge pressure because this gives a water reserve of a litre or two in the EV to make up for any collapsing air bubbles or tiny leaks and avoids frequent top ups, if the pre/filling pressures are the same then top ups will be frequent. But because your EV is so small you cannot have the filling pressure > than the precharge pressure by more than 0.25bar without lifting the PRV when the system heats up.
If you had a 18 litre EV, with pre&filling pressures of 1.0/1.5bar. giving a water reserve of 3.6 litres and a final pressure of 2.48bar, the 10 litre gives a reserve of 1.25 litres & a final pressure of 2.72bar with pre&filling pressures of 0.75/1.0bar.

 

[Elraoak]

Correct, the pre charge pressure is the EV air/nitrogen pressure before installation but should always, without exception, be checked/corrected with a pump/pressure gauge. The filling pressure is the pressure that the system is pressurized to while cold by opening the filling valve. The filling pressure should always be 0.5 to 1bar > the precharge pressure because this gives a water reserve of a litre or two in the EV to make up for any collapsing air bubbles or tiny leaks and avoids frequent top ups, if the pre/filling pressures are the same then top ups will be frequent. But because your EV is so small you cannot have the filling pressure > than the precharge pressure by more than 0.25bar without lifting the PRV when the system heats up.
If you had a 18 litre EV, with pre&filling pressures of 1.0/1.5bar. giving a water reserve of 3.6 litres and a final pressure of 2.48bar, the 10 litre gives a reserve of 1.25 litres & a final pressure of 2.72bar with pre&filling pressures of 0.75/1.0bar.

I looked up the volumes of the column radiators (and made a few assumptions on the ones I couldn't find) and the volume in the radiators alone is 200-220L. It's only 12 rads (Inc. towel rails), but changing some of them from panel to column has nearly tripled the volume in some cases.

Then there's 70-80m2 of wet underfloor heating on top of that.

18L may not be enough?

 

[John.g]

Say 50 litres water in UFH = total of 270 litres, also the expansion vol for ufh is far less than for rads because of the lower temperatures. however plan for 270 litres at "rad" temperatures. 18 litre EV, pre&filling pressures of 1.0/1.5bar = final pressure of 2.62bar. 24 litre EV = final pressure of 2.26bar, if space no problem then why not install the 24litre?.

 

[Elraoak]

Got to find someone who can install one pronto as we are moving soon and trying not to leave new owner with these recent occurring problems! Typical we start having issues just before we sell (and have been trying to fix for the last 5 to 6 weeks - just running out of time).

Hadn't appreciated the need to preload the EV with water to allow for temperature drops. Given the boiler cuts out at 0.8bar it would make sense for the precharge to be roughly the same, so it's emptied out before the boiler shuts down.