Tower ABV (ABBV1)

[adrian109]

Hi,

I have a Worcester Bosch Greenstar 32 CDi Natural Gas boiler.

The system is fitted with an external Tower Automatic Bypass Valve (ABBV1).

I need to work out what setting (1-6) to adjust the external automatic bypass valve to.

I can't find the minimum flow rate for the central heating mentioned on any of the boiler documentation.

I believe I need to know this plus some sort of pressure (looking at the chart on the attached instructions) to work out what number setting to use.

Is anyone able to help me work this out please?

Many thanks.

 

[Johntheo5]

Have a look at your MIs, if you have a eCopy post it on here, your circ pump will/should have several options like the attached, you can see which one yours is set to, once you know that then its relatively easy to set up the ABV.

 

[adrian109]

Do you mean this chart?

 

[Johntheo5]

Yes, but a constant pressure setting shouldn't be used with a ABV as it depends on the pressure (head) increasing as the flow decreases which can only be achieved with a pump running at a fixed speed, option 0 is variable speed (depending on boiler output I think) but even though this can/should be able to be clamped at a fixed speed it can be difficult to figure out the settings, what you can try is, set/leave the pump on setting 4 which is 0.3bar, 3M, and set the ABV initially at 0.4 on its index, when the boiler is running and up to temperature the outlet (bypass to the boiler return) from the ABV should remain cold/cool, then very slowly keep turning the adjusting knob anticlockwise until the ABV outlet starts getting hot then turn the ABV adjusting knob clockwise say 1/2 a turn or so and see how it goes at that. Have you got a link to your particular boiler, if so, post it on please.

see above settings again

 

[Johntheo5]

Is the Boiler you have the CDI compact combi boiler?, if so, this has a internal bypass and unless you have TRVs on all the rads I wouldn't be too worried re the ABV but you can play around with it as suggested, just start with a high index setting. This boiler outputs 32kW to DHW and 24kW to CH with a minimum output of ~ 6.5kW.
The MIs file I have is too big to download but this should identify it.

 

[adrian109]

Yes, I have the Greenstar 32CDi Compact ErP, model number: 47-406-79.

I have 10 radiators on the system all of which used to have standard TRVs apart from 1 standard radiator and 2 towel rails.

I have since changed the valves on those remaining rads to TRVs, plus I have removed the TRV heads and replaced them with the Tado X Smart Radiator valve heads.

I read by doing this I should add an external automatic bypass valve as the system has the potential for all the TRVs to be closed at once increasing the pressure and potentially damaging the pump/boiler.

So that is why I fitted the external Tower ABBV1 automatic bypass valve to bypass in the situation of all TRVs being closed.

But now, I'm trying to work out how to set it so that it only bypasses when most of the TRVs are closed.

I have attached 2 documents:
Greenstar_CDi_Compact_Combi_ErP_Installation_and_Servicing_Instructions - split into 4 PDFs to upload
Greenstar-CDi-Compact-Combi-ErP_Installation_Commissioning_and_Servicing_Instructions - split into 4 PDFs to upload

 

[Johntheo5]

OK then, the only in theory "perfect" way is to open up all the rads (TRVs etc) to give full circulation, then check what mode the pump map is on, check the actual pump speed in %, then change to mode 0, 3-d1 which is variable speed mode depending on the boiler output, no good for your ABV,but you can "convert" this to a fixed speed, if the actual speed was say 60% with all rads open (and Hot) then set 3-d3 to 60% and 3-d4 to 65%, you then have, in effect a fixed speed pump which should make the the ABV setting up easy!!, however the fly in the ointment is the boiler's internal ABV, which may still open depending on the pump head so even though the rads flow and return may have a nice dT of say 15C to give reasonable condensing (if flow temp is 60C) the internal ABV might result in a boiler dT of only 7/8C reducing the boiler efficiency. IMO if your 2 towel rads don't have TRVs then those, together with the internal ABV should give adequate circulation with the external ABV shut off at index 0.6. Anyhow see how you get on, just note any pump mode/settings before making any changes.
I havn't read your attachments yet but will later.