Air Problem in Open Vented System after Boiler Change

[Last Plumber]

Also forgot, the condensate trap on the boiler seems to run quite often and has a black/dark dusty sediment in it. Is that normal?

It's normal to have a small settling of dark residue in the bottom of the trap if that's what you mean? It should be cleaned out at service time.

How is the Flow to the Cylinder Coil vented? (curious).

 

[Last Plumber]

Could a faulty hex explain foamy water in the primary circuit?

Too much inhibitor could do in my experience. It can be overdosed and end up like soap as it leaves the pump. Only seen it on very few occasions but it can.

 

[fixitflav]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Just one thing, probably irrelevant to your problem but I'm curious. You said earlier the Evohome controls the hot water, and I can see in the pic the actuator has been removed from the HW valve. How does that work? What stops the HW getting too hot when CH is on?

 

[ThePook]

It's normal to have a small settling of dark residue in the bottom of the trap if that's what you mean? It should be cleaned out at service time.

How is the Flow to the Cylinder Coil vented? (curious).

Yes, that's what I mean about the trap - thanks for confirming.

The DHW primary coil had a manual vent on the top (flow) connection until this evening. I have fitted an AAV there tonight and on the top of the return to the boiler. Let's see, but not optimistic!

Too much inhibitor could do in my experience. It can be overdosed and end up like soap as it leaves the pump. Only seen it on very few occasions but it can.

Interesting, I have 1l of X100 in a 10 radiator system. Tested it with Sentinel's Quick Test kit, and looks spot on.

Just one thing, probably irrelevant to your problem but I'm curious. You said earlier the Evohome controls the hot water, and I can see in the pic the actuator has been removed from the HW valve. How does that work? What stops the HW getting too hot when CH is on?

The missing actuator is the CH flow, so the valve is full open. The HR92 radiator valve controllers open/close to control flow to each individual rad. If you download the Evohome manual, it is their preferred 'figure 4' installation. Works well, and means each room is a separate zone with time and temperature control. The right-hand BDR91 in the photo opens/closes the DHW zone actuator (mine is also hardwired via a conventional cylinder thermostat, so for safety it does not rely entirely on wireless control to limit water temperature). The total heat demand is calculated by Evohome and is controlled by the left-hand BDR91 wireless boiler relay in the photo.

 

[fixitflav]

The missing actuator is the CH flow, so the valve is full open.

OK, not for the 1st time, I jumped to the wrong conclusion!

 

[ThePook]

Ok, so tried a few more things:

The air can be purged out of all circuits if it is run with the boiler off. I can achieve silent flow whichever zones are open in this way.

If I fire the boiler, as soon as it reaches temperature (currently flow is set at 70C) I hear air bubbles coming out of the top of the boiler and through the pump.

If it is circulating through DHW or Auto Bypass Valve at the time, I get quite a large overshoot on the flow temperature (approx 8-10C) before the boiler modulates down. I am sure this is to be expected, as in either of these scenarios, the return temp is higher. But I guess it might explain why the noise is worse after either of these circuits have been active.

Thoughts?

 

[fixitflav]

Ok, so tried a few more things:

The air can be purged out of all circuits if it is run with the boiler off. I can achieve silent flow whichever zones are open in this way.

If I fire the boiler, as soon as it reaches temperature (currently flow is set at 70C) I hear air bubbles coming out of the top of the boiler and through the pump.

If it is circulating through DHW or Auto Bypass Valve at the time, I get quite a large overshoot on the flow temperature (approx 8-10C) before the boiler modulates down. I am sure this is to be expected, as in either of these scenarios, the return temp is higher. But I guess it might explain why the noise is worse after either of these circuits have been active.

Thoughts?

With those symptoms, it looks to me more and more like the h/ex. Maybe something expands when it's firing, causing a leak to open up. On the optimistic side, maybe there's a bolt or something loose, which can be easily fixed.
Presumably the boiler is recently installed so still under guarantee. Have you involved Intergas? I still think I would replace the h/ex, at their cost, naturally, if it cures it. It's not going to be that expensive, in the context of the problem, if it doesn't. You seem to have eliminated everything else.

 

[Dave M]

Sorry, don't understand that, is it something I said?

Cold feed from tank should be fitted in return ,on the photoits in wrong place. so cap off by air separator and connect to return at bottom of picture

 

[fixitflav]

Cold feed from tank should be fitted in return

That's how it was done 40-odd years ago, nowadays it's boiler - open vent - cold feed - pump. Cold feed preferably up and under, to avoid convection warming the F/E tank, hasn't got that here, but I doubt it's causing the current problem. Earlier arrangement caused seesawing between the vent pipe and the F/E tank, drawing aerated water into the circuit every time the pump starts and stops.

 

[ThePook]

Hi all,

Apologies for the long gap between posts, but I have let this run for a couple of weeks with the flow temperature at 65degC. The result - total silence.

On Friday night I turned it back up to 70degC. The bubbles are back with a vengeance!

The boiler manufacturer's customer service have not been helpful at all, which when you consider the cost of a boiler is very disappointing. Wondering if I might end up forking out of my own pocket for my GSR installer to fit a new heat exchanger, but considering the lack of interest from the manufacturer, I feel like I would rather put the money towards a different brand of boiler altogether.

Any other thoughts before I bite the bullet?

Thanks in advance all.