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Mysteryman I quite agree - simple but safe, including equipment protection! I have actually just 3-4 days ago installed the weather compensation VR430 etc and am full of hope you are right. The 'unload rads' I have are "inside the zones" and rightly or wrongly I worry about boiler flow...

Here are links to the presettable flow controller advised by Grundfos. About £35 from Plumb Centre, though they had to order from their central stores. Took half an hour and a 24 mm spanner to install - a bit less in time, cost and bulk than Agile's LLH etc...

My Lord Hailsham An admirable summary! What I've actually done is retain the auto bypass set to open at just above top press of my pumps autoadapt zone. I have aimed at 3.9metres! this is really just to cover "emergency" situations. You could argue I should set it just below the 3.8metre[max...

A lovely simulator! Thanks - I am playing with it now! smokebox

Blimey! How clever! I will start evening classes Problem is the German versions will probably vary as well, even if you could find them, though the linguistic / translation variations would hopefully be absent. smokebox

So what bypassing do most 'thinking' people use? Do they just settle for an autobypass set near upper end of the grundfos pumps Auto modulating region from their Q/mtrs output chart, but just below the top pressure reached in autoadapt mode? smokebox

David and Upgrade I think you are both right here in a way. My system is almost exactly like modokon's except I have an ordinary domestic vented cylinder (though quite modern and 'fast'. - actually 2) It is clear that the VRC430 / boiler between them compute a target flow temp related to...

Nor address this specific matter, nor the answer to the bypass for ordinary running versus overrun.! smokebox

My lord in a previous thread "What do modulating pumps do", you asked for Manufacturers. Instructions stating in black and white what this minimum flow rate might be for this purpose. It is NOT stated in the Vaillant 415 to 438 MIs! I have however email correspondence from Vaillant...

Lord Hailsham I stand corrected! Indeed that pump (15-50)oddly is not listed on that link. Apologies and I can't think why it is omitted! I think it is a newish pdf, and maybe that particular pump is going to be withdrawn. I can't exactly give you a link to 15-50 Data, but I have had some...

Jonas Ah I thought only of Google - i'll wake up shortly! Smokebox

Can anyone contemplate all this, and make some observation to assist a foolish dolt? smokebox

Jonas Thanks. Others have also mentioned the Geminox, and it sounds interesting with its very low modulation capability. Their 2.4 to 13.5kW looks well sized for many UK houses. I gather it is French, and distribution/spares/service staff knowledge in UK is quite an issue. I have not really...

Yes Agile I was interested in those ++ especially since Vaillant boiler behaviour was being examined. For the modern well insulated smaller house 5kW down modulation is not low enough to avoid cycling of one sort or another. As I mentioned before I was worried about this issue here because...

well Dan I have you suggeting the boiler is too small (am I right?0 and Agile thinks it is too big. I think it will do.! Yes I am iin danger of obsessing too much over the bypass, but I really hate to see man designing a really clever condensing boiler, then preventing or reducing...

Agile most of the time everyone's boiler is overpowered for their heat loss. They actually have to be! Smokebox

Agile Please do not take too much offence at my little anti Vaillant and anti numpty rants! In all truth Vaillant really were ignorant and rude in my view. I have a little intelligence, admittedly only a little but it seemed better in understanding the physics of energy transfer...