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Thanks, yes I did notice that after turning off the left hand boiler (the one with less controls) its heat exchanger was still nice and warm! So I closed the isolation valves as you say and they immediately started leaking! They are 20 years old. So a good thing to make sure of, but still...

I hadn't heard of Intergas, they look perfect don't they - the hot water is done with valving in the house so the Hre Sb 40 should be fine, and what a price! Edit: oh it's a System Boiler. Damn! I did the online energy calc thanks, it said (edit) 17.7kW (done more carefully than my first try...

Thanks, yes, I'm thinking it has to be both but a bit more the flow, as much as anything, because the boiler itself is getting up to temperature alright and cycling on and off. The rads nearer the boilers get hot, then the farther ones only warm even wide open and with the upstream ones...

I'm in Norwich. If you did know someone that would be great. This system has had at least 3 'qualified' heating engineers on it and apparently none of them really clued up. It's been in 20 years and never really worked properly I think - never been balanced because it just won't! I like the...

Thanks, yes this is definitely steering me away from this twin boiler concept. It's like parts of the system have been done professionally and some haven't. Or professional/cynically! It is a big house and so I think I'll want the power to warm up in a reasonable time, a bit more than 28kW...

The pumps: Looking it up, it's 250mbar.

Take 2 with the photos. Vaillant twin boiler pipework. Working upwards it’s Return, Flow, Gas.

Okay good point about the head, thanks. It's quite a rambling system as well as tall. No I have no numbers for the heat loss I'm afraid. It was not balanced at all, one turn on each lockshield! Bit of a disgrace really. But I have since done it to some reasonable extent. Here's the pipework...

Yes, it seems weird to me, but I'm just a kind of DIY engineer. As far as I can see, the second pump is trying to pump into a flow that's already been pressurised by the first pump, so the system is a big heat system with a little pump, in effect.

Well the heating capacity isn't the problem. In fact they're both turned down to 20kW, the latest engineer said. It's the flow.

Hi all. I've moved into a 3-storey house, with the highest radiator 8m above the boilers. There are 30 radiators including towel rails, served by two 28kW Vaillant 628e boilers connected in parallel, i.e. each across the return to the flow. They're system boilers each with a standard pump that...