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Not with this controller, that's a feature of the newer ones. Mike

Thanks for explaining that, although as a humble electronics engineer I'm afraid hydraulics is not in my comfort zone ... Regarding the controller's behaviour I'm not the only person who has had this problem. If you look at the first graph on this page you will see the same thing happening...

At the moment (without OT control) when the boiler is running at 5kW the flow and return temperatures are 65C and 57.2C, giving a flow rate of 9.2L/min. Mike

As I've decided to stop playing with this for a while I thought it would be a good time to summarise my experience with the Vaillant VRC 470f weather compensating controller. This graph best illustrates the problems I've been having: My observations: 1) The HW cycle works just fine. The flow...

The gate valve has a square spindle. Is it really OK to run the pump with its output completely blocked? Sadly I've run out of time to do this as we're going away shortly and the other jobs are piling up. I may just give up on weather compensation altogether and put the old (VRT 392f)...

Sorry but what is a pump discharge valve? Do you mean the gate valves either side that shut off supply when removing the pump? On the graph above (13th April) the OT was 6C and the heat curve was 2.5, giving a desired flow temp of around 60C. Under these conditions the desired flow temp dropped...

Thanks for this, but not sure what to do with it! Mike

Ah that's good then. I hope the build goes well. Mike

OK after a couple of days away I started again with a clear head and this time got sensible results. I switched off the boiler, connected the pump to a separate supply and operated the zone valves manually. The results were the same whether HW or CH was selected: I - 29W II - 43W III - 56W...

Hi Harry, can you get hold of those boards? Last time I checked on john30's discussion group they weren't available but I may be wrong. The advantage of the ebuzzz adapter I built is that there are no adjustments and it works perfectly with Vaillant boilers. The disadvantage is you have to be...

Thank you for explaining that. When I get home later I will try to measure the pump power again. I know the meter is OK because it measured down to 1Watt on another device. Mike

Yes I will check the pump when I get a moment. Thanks again for all your advice, I've learned a lot! Mike

Well it turns out that I was on a wild goose chase with this. I was about to test the pump as you suggested when I noticed that the CH zone valve was stuck half open; the return spring in the actuator was broken. I replaced the actuator, set the boiler back to Flow regulation and the Anticycle...

I have one of those monitors, that's a great tip. Thanks for all your advice, I really appreciate it. I will speak to Vaillant at some point but they will probably want to sell me a new boiler ... Mike

It's a Honeywell. Just one more question before I leave you in peace. Given the age of the boiler (2009) is there such a thing as a software upgrade or replacement control board that might improve its performance? Mike

I should say that 3 radiators are usually off unless we have people staying. I tried the pump on setting 3 but it didn't seem to change anything. Should I adjust the ABV? Mike

Thanks. It's a 1970s 4 bed detached house with 10 rads. As far as I can tell by touching the pipes the ABV is not open when the boiler is running. Mike

The pump is a 3 speed Grundfoss UPS2 15-50/60-130 on speed 2. The ABV is just below 3.5. Mike

Thank you so much for you detailed explanation. This boiler is a bit of a mystery to me even though it was installed in 2009! The manual specifies a minimum flow rate of 12.9L/m. Is this proportional to output, i.e. 6.5L/m at 50% power? The ABV was changed in December as my heating engineer...

I set d.00 to 12kW and on the next CH cycle at 1200 hrs it reached the (albeit lower) desired temperature. I shall have to wait until the morning to see if there is something else stopping the CH flow temperature from going over 50C. I have a long (60 minute) anticycle time to prevent short...