Trianco Aztec 4kw boiler question

[Madrab]

if the diapragm has gone in the expansion vessel then the air would get released through the auto air vent.

and then the pressure would rise to over 3bar and the PRV would open?

 

[Madrab]

Just checked the boiler this morning and the under pressure failure light is lit.

as @snb1 suggested have you checked the EV pressure to see if it's holding pressure?

 

[Jethrosax]

I measured using my tyre gauge and the pressure appears to be well down, it’s ver awkward to get in there and some air seeped out but it didn’t drive the gauge to where it should be. As the pump housing only leaves an 8mm gap to get a gauge in, therefore to get an accurate reading I need to remove the pump which means draining the system, that I plan to do after I return from a trip into my local town.

Next installment in a couple of hours or so!!

Jethro

 

[Madrab]

If the EV pressure has dropped again then @snb1 suggests, the (edit) air from the EV isn't being retained and it's being released out into the system as the pressure rises and then being vented out of the AAV. Once that happens though there should be no air left to absorb the expansion and would expect the system pressure to rise up to the PRV opening point again ~3bar.

 

[Madrab]

Just another though too, you do get 2L EV's similar to the one that is in your system - depending on connection and overall size you may be able to get a direct replacement.

 

[Jethrosax]

The pressure never rode above 1.5 bar yesterday when the boiler was operating and then fell back to 0.8 bar after being off for a couple of hours. I’ve been looking ar replacement EVs and haven’t found one yet. The coupling measured with a calibre has outside diameter of 21mm. Will need to get it out to be sure.

Jethro

 

[Jethrosax]

Really puzzling I have now drained the boiler and removed the pump. The EV shows 0.85 bar which given that there was a slight leakage when I attempted to measure it with my tyre gauge suggests that it may have been OK. Have now topped it to 1.0 bar.

Before doing that I opened the isolation valves and noted a slight rise in water pressure really slight but a rise not a fall so that’s not likely to be the source of any leaks. Prior to drain down I noted then the pressure was still 0.8 bar as it had been since early morning so I think therefore that the PRV is not leaking and there’s no evidence of water anywhere around the unit.Clutching at straws, but there’s no water in the system and the pressure guage is not showing zero, see attached. Could that be causing me to fill to the wrong pressure in the first place I wonder?

If I leave the EV overnight at 1.0 bar and check again in the morning and it’s still reading 1.0 bar with no water in the system does that prove it’s ok.

Your thoughts would be appreciate.

Jethro

 

[Madrab]

Tap the gauge, they sometimes stick. I wouldn't expect the system to lockout until it dropped below 0.5bar not 0.8 bar, so the gauge may be a little sticky. If the EV still has 0.8 bar in it on a depressurised system then chances are the membrane isn't compromised but yes if you leave it overnight and the pressure stays the same then the EV.

So if the EV pre-charge is fine and holding, the pressure doesn't rise in the system when it's warmed up, the PRV isn't passing water outside then there is very little else that could be releasing water apart from the system somewhere but that's been tested too.

If you can remove the pump then the EV should just unscrew and lift up and out. All it needs is some PTFE tape to replace, would make it much easier to size up and check if it's holding pressure. It may not be needed though if it does hold pressure. You'll need height/width and thread size.

 

[Jethrosax]

To eliminate things I’ve ordered a new pressure gauge should arrive tomorrow. Having tapped it, the needle doesn’t budge, so probably best to have one that might be more accurate. I’ve had a go at removing the EV but it won’t budge, so I’ll have to use an oil filter removal tool or a strap to get it moving. Reading other blogs it seems that EVs generally only are good for five or six years, so after 13 it’s probably best to change it if I can find a replacement even if the pressure appears to be holding. It’s well sealed in with ptfe tape.

Jethro

 

[Jethrosax]

EV now removed see photo. It’s a zilmet unit appears to be still available so one has bee ordered. The unit unfortunately brought part of the fitting with it so will wait for new unit arrival before attempting to remove it. It was well lodged in to it’s fitting, but removed without damage using an old engine fan belt.

Contemplated ordering two units but that might be trusting to luck.

Jethro

 

[Jethrosax]

A question. The replacement EV arrived this morning and the shipped pressure was 3.7 bar. The EV that I removed shows 1.0 bar after 48 hours. I’ve just upped it to 1.15 bar and if that is still holding after 48 hours would it be best to re-use it or fit the new one which is from Italy?

I’m attempting to source a new pressure gauge as when at zero pressure it shows 0.5 bar so not helpful.

Jethro

 

[Madrab]

Well if the EV is holding pressure without loss, off the jig, then there can't be anything wrong with it. Wouldn't be any reason not to re-use it IMO.

So it's back to :-
No EV membrane issue so no air being released through the AAV and the pre-charge pressure is properly set
No over pressurisation of the system whilst running (new gauge will confirm), so PRV should not be lifting
No visible water inside the unit or around the external valves etc
Definitely no water being found at the PRV outlet outside?? This would really be the only other suspect, as part of the unit

If that's all good then it HAS to be out on the system, as absolutely everything else has been ruled out.

 

[Jethrosax]

Thanks, I think the original problem was the EV as there was at the time zero pressure in it when tested. As it’s holding pressure when outside the boiler as you say it’s probably good to re-use. On another thought I am trying to source a pressure gauge as I think that maybe, as it reads 0.5 bar with no pressure in the system has led me to set pressure too low and when the water cooled it dropped below the “low pressure” alarm threshold. There’s no indication of any water loss in the underfloor pipes though otherwise your conclusion seems right. Bit of clutching at straws at the moment. Anyway ripping up the concrete floor is definitely not a way to go and when put in I insisted that only one continuous length of butyl pipe was used to minimise the likelihood of leaks.

Jethro

 

[Madrab]

Bit of clutching at straws at the moment

it may seem like that but fortunately it's not, there are a finite number of things that it could be and fault finding is about working through them to find the problem.

On another though I am trying to source a pressure gauge

I’ve ordered a new pressure gauge should arrive tomorrow

You said you had one on order?

You want one of these - Trianco Gauge - 501808 (0-4bar 1/4" BS 557-2) - https://bhl.co.uk/pressure-gauge-557-2-0-4-bar-14-bs-trisp501808.html

 

[Jethrosax]

Yes it arrived this morning but the rear thread is too small it’s 1/8th mbsp and the very helpful man from Watts suggested getting a boss as the unit I’ve taken off is 3/8. Watts have the one I need but it’s from Bulgaria minimum order qty 300 he suspects.

Just spoke with BHL thanks for finding that brilliant if it’s the correct one. I did speak to the Trianco spares person earlier in the week but he wasn’t very helpfu. Anyway if Neil from BHL can confirm the rear thread is 3/8th bsp (very unusual) and probably Monday now then I can order it and you’ll be my hero.

Jethro