Air getting into upstairs radiators. Possibly caused by kettling?

[nick_a_louse]

Could you (if installed) extend the pump overrun time to say 5 minutes, shut the ABV (if installed) and then open the zone valves manually once you shut the boiler down??.

You can set it all right but if you do decide to do the test ensure all air is vented first. It actually defaults to 5 mins but you can extend that to 10 or 15 minutes to do every thing at your leisure.
All you have to do after extending the overrun time is to ensure boiler running then turn roomstats down, the burner will stop firing and pump overrun commence.
View attachment 73026

So I was finally able to get some time to play around with the boiler (set the overrun to 10 minutes).

After a short period, the radiator was quiet, and no kettling-like noises from the boiler (just the hum of the pump).

So my understanding is that the water continues to flow as normal during overrun, to help draw heat out of the heat exchange etc. I guess this rules out air ingress through the pump etc, and makes the main heat exchange the only remaining candidate. Correct?

Anything else worth considering before I start looking at quotes? Still going to be cheaper than a £2-£3k for a new boiler + labour

 

[John.g]

Presume you manually opened zone valve(s) once pump overrun commenced? If so, would possibly point to Hx problem, if so, unlikely to be scaling problem as it's the primary Hx, partial blockage, unlikely, maybe inhibitor causing problems? Just dont know. You could just drain the whole system down, refill, do not add inhibitor and see if problem persists. When (if) you do this and if problems the same, suggest giving Vaillant a tincle and see what they say, they may have a fixed price for Hx renewal, the fixed price might also include a general boiler check out.

 

[nick_a_louse]

Presume you manually opened zone valve(s) once pump overrun commenced? If so, would possibly point to Hx problem, if so, unlikely to be scaling problem as it's the primary Hx, partial blockage, unlikely, maybe inhibitor causing problems? Just dont know. You could just drain the whole system down, refill, do not add inhibitor and see if problem persists. When (if) you do this and if problems the same, suggest giving Vaillant a tincle and see what they say, they may have a fixed price for Hx renewal, the fixed price might also include a general boiler check out.

Re values during pump overrun - yes, I popped off the TRVs to ensure they stayed open.

I managed to find time over the weekend to drain everything down (except one rad with a seized drain point). Refilled with no inhibitor, but so far it seems just as noisy after 24 hours.

I had a look on the Vaillant website, they seem to outsource all their servicing to third parties (one of the 'MasterTechs' has actually already been here, with little helpful advice except to do another power flush). I'll try and call Vaillant, and see if they have anything else to offer.

Thanks again for the suggestions- will update this thread, in case someone else has a similar problem!

 

[John.g]

Only other items that may cause noise are the TRVs, some makes like Tower seem particularly noisy but some of the better known ones have caused noisy operation as well,I have mine installed horizontally on the rad returns so the water flow is from under the valve seats, bi-directional are supposed to operate in either direction.

If you have a schematic of your boiler, you might see where the expansion vessel is installed, ie, before the circ pump or after it, if no schematic ask the installer, you can,t do anything about it in any case, shouldn't matter as long as the E.vessel pressure is 0.75 bar or greater when cold which yours is.

If the boiler CH temp is set to its minimum of 35C/40C, is it still noisy?.