20°C differential between flow & return is optimal for condensing boilers, so this is a bit wide but not too far out, certainly not enough to suggest lack of power. Much more likely to be lack of flow.
Twin system boilers not up to it?
- Thread starter Nigel R
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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 balanced. Also it's losing some temperature even in the 35mm pipe. I'm thinking the system is basically misconceived, as though the Vaillant dealer didn't have a big boiler on hand but a couple of 28kW system ones on the shelf
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 that yielded 36), tho in this old house it's really approximate of course, but either way that boiler should do the job nicely, I think. And with that pump, more saving and more power! Thanks so much
It was a never ending battle last winter, actually changing to a thicker rug, on the sofa!
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If they work no need to replace the Vaillants. The boiler room needs a proper repipe and a header fitting with a dedicated system pump.
The only question about having two boilers is whether there's enough gas to run them
The only question about having two boilers is whether there's enough gas to run them
As a temporary fix to get both boilers working, can you change the flow temperatures so boiler 1 gets input 40 and output 55 and then boiler 2 55 to 70? That way you might get both pumping and heating.
Agreed you need a low loss header designed into the system by a commercial heating engineer.
Agreed you need a low loss header designed into the system by a commercial heating engineer.
To be honest you'd probably get a lot more heat out of the system as it stands by turning the second boiler off and closing its isolation valves.
You are almost certainly losing the remaining head from the boiler pump due to reverse circulation.
Nothing to lose by trying it for a couple of days but I think you'll be surprised
You are almost certainly losing the remaining head from the boiler pump due to reverse circulation.
Nothing to lose by trying it for a couple of days but I think you'll be surprised
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 only a tepid last radiator unfortunately. (The leaks have gradually subsided)To be honest you'd probably get a lot more heat out of the system as it stands by turning the second boiler off and closing its isolation valves.
You are almost certainly losing the remaining head from the boiler pump due to reverse circulation.
Nothing to lose by trying it for a couple of days but I think you'll be surprised
And yes a header. A new thing to me and definitely something to look into. It seems they can be great or not, depending, and with two boilers a necessity, or with one new condensing and modulating boiler running a single circuit possibly not?
The issue you have (as I think it was Muggles said but might have been someone else) is that by the time the water has been pumped through the boilers there isn't enough horsepower left in the pump to go all the way round the system.
A header doesn't have to be a massive commercial thing it's a pretty straightforward way of hydraulically isolating the boiler flow from the system flow.
A small header with a reasonable sized system pump after it, couple of non return valves on the boilers and a good balancing of the system and you should be sorted
Ps sorry about the valves
A header doesn't have to be a massive commercial thing it's a pretty straightforward way of hydraulically isolating the boiler flow from the system flow.
A small header with a reasonable sized system pump after it, couple of non return valves on the boilers and a good balancing of the system and you should be sorted
Ps sorry about the valves
I've sent the guy a message, i have a lot of these setups in norfolk running on low loss headers. Gianonni exchanger has a lot of resistance and is normally only able to cope with about 12 rads max without some fine balancing. putting a low loss header in with a 8m pump normally will be fine for up to 30 ish rads. But more often the system can also benefit it can be zoned
Thanks so much for all the help everyone. I have all your advice in mind but also I've started to suspect a pair of double vertical radiators at the end of a run might be too cheap/faulty/upside down. No label on them. So I've put it down for the moment, while I sort out some other parts of the system, including one I'm asking for advice on in a new thread. And yes snb I plan to give you a call thanks.