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Will do.

Thank you once again John. Presumably the set flow temperature is immaterial for these tests, which I will do as you suggest? I have to solve this problem of why the ABV is passing flow when it should not be. One thing I have thought of is that, once I have cleaned up the innards of the old...

Afraid I'm back again because I was too hasty in concluding that my replacement ABV was working properly but, unfortunately, I still have the same issue with continuous circulation via that valve. The valve is set to 400mb and the boiler pump is on constant pressure setting 1 at 150mb. So my...

I guess the fact that I used a WB accredited installer and that gives me the 12-year warranty, means they will sort any issues with the boiler, even if the cause lies elsewhere. If it is the installer's fault, WB should take the matter up with them, as I can be said to have done “all due...

Yes, one would have hoped for better temperature correspondence. The sensing arrangements don’t seem to be very satisfactory. But at least we now have good performance back and won’t be short of heat the next time it turns really cold. Only question is will the issue recur? They did check...

Hi again John. I can’t see anything in the Installation and Maintenance Instructions about the HEx head loss. The only thing in the specs is “Available pump head at 20C system temperature rise = 2 metres” I’ve done a set of readings at 60C set temperature but could try to do some at 70C if...

Thanks John. I'll have a look in the instructions. Yes, it does seem strange that they are not sensing the real flow temperature more reliably (and they don’t sense the return temperature at all!). Afraid I didn’t design the boiler!

Hi John. I’m afraid I didn’t see your message earlier, as the engineers arrived just before 7.30am. They have just left after replacing the HEx. Actual flow temperature now equal to or above(!) the indicated flow temperature. Rads too hot to touch now, so I will be able to lower the set flow...

Hi Johntheo5. Boiler has been running for a while (heating only) so I’ve taken some readings at pump setting 2, ie 200mb. Target flow temp set: 70C Indicated flow temp: 71C Actual flow temp: 56.4C Actual return temp: 44.4C Burner modulation: 19% (6kW) Pump modulation...

Thank you Johntheo5. I will also respond further later today. The pump is currently on 200mb but can easily be changed. However, the ABV is set to 400mb, so I wouldn’t want to cause that to open. More later.

By way of update ………. The faulty external ABV has now been replaced and the new one is working correctly, stopping the unwanted flow that was short-circuiting flow water to the return side of the boiler. Some of the moving parts of the old valve were stuck due to a build-up of black deposit...

Thank you Johntheo5. Yes, I have also been thinking in terms of scaled waterways in the HEx, rather than really clogged up. Once one thinks in those terms, and recognising that the supposed flow temperature sensor is not fitted on or inside the actual flow pipe as it leaves the HEx, but seems...

Hi Johntheo5, have done the measurements and here are my results: First set are at pump map 2 (200mb): Target flow temperature set: 70 Indicated flow temperature: 73 (Actual flow temperature: 57) Burner modulation: 21% (6kW) Pump modulation: 58% Second set are at pump map 6...

Thank you Johntheo5. Will do when a get a bit of time. Trying to keep all my life balls in the air! Have been in communication with my installer about the ABV ……….! (On a conventional open-vented system and boiler, I would happily dive in and change the valve myself but I’m not used to...

Thank you dilalio. We actually went for by far the most expensive quote with a personally recommended company that is Worcester Bosch accredited to the 12 year warranty level. It was also the company that instilled the greatest confidence in us after extensive discussions with several about...

Thank you again Johntheo5. Yes, that was my conclusion (before getting back to WB about the flow temperature issue and a possible HEx replacement). I will take those readings you suggest (plus my true flow temperature measurement!) and then post back.

OK Johntheo5 …… ABV set to 0.6 (600mb+). Boiler started by raising room stat for one heating circuit. Pump at 150mb; wait 5mins; Pump modulation 46% and rising slowly. Pump at 250mb; wait 5mins; Pump modulation 63%. Pump back to 150mb; wait 5mins; Pump modulation 50%. Pump back to 250mb; wait...

Thank you Johntheo5. I will do that and post back. Meanwhile, glad to hear you have the same suspicions as me!

Thank you Johntheo5. Yes, I followed all that on the Buildhub thread but am not so worried about the indicated flow temperature sometimes being a bit above the set flow temperature. My big concern is the actual flow temperature being unable to reach the set or indicated flow temperature by as...

Thank you Johntheo5 and Mister Banks for your replies. Firstly to Mister Banks, thank you for pointing me to the thread on Buildhub, which I see is not only on the same issue but was actually started on 15th December by the same person (GeddyMortgage) about the very same boiler and issue as...