Which modulating system boiler?

[Razor900]

Not had much to do with J&S cos I don't like warm air, might see if they do free training though

If you fit a Biasi do your bit for customer service, give the custard Agiles number

 

[transam]

Do not purchase biasi boiler's any more , fell out with them , decent product lousy company to deal with , some of there service agent's , (note the wording some ) are a nightmare !!!

J&S do free training , I was booked in on the same day as the B.G strike that never took place , it got cancelled , think I am there in June .

 

[D_Hailsham]

Assume I could just order one from Netherlands

Be careful. Check that the Display and Instructions are in English

Holty, it is a good question but my assumption is that with a Heatrae Sadia Megaflow 170l, not huge consumption of HW and good recovery time the majority of the burner action would be for CH. I have not checked but in S-plan if the CH is modulating and the HW calls for heat I assume because not modulating signal the burner would hit high....correct me if anyone knows better.

Remeha use a diverter valve the "wrong" way round, so the heating circuit is the normally open one. When the HW thermostat calls for heat the valve switches over, so only the HW circuit is in operation and, at the same time the boiler is ramped up to max output.

WB do the same on the 30CDi system boiler if you fit the optional diverter valve and use the FW100 controller.

Viessmann do the same.

Thinking logically, any weather compensated system must be able to ramp up the boiler temperature when HW is called for, otherwise the temperature may not be high enough to bring the cold water up to 60C.

 

[bluyeboy392]

Remeha use a diverter valve the "wrong" way round, so the heating circuit is the normally open one.

Something to bear in mind then; if it uses a diverter valve then don't they have a mid position when both CH and DHW are calling for heat? What would it do then?

Sounds logical too about HW because if modulated to lowest setting the water in the system wouldn't be anywhere near 60C I guess. Worth checking wiring / layout for this then.

On another note I had been recommended a Baxi 28HE system boiler which apparently "on most models this [is] done by varying the fan speed which will increase /decrease the gas rate as it speeds up and slows down". Does this sound reasonable? Is this just a really ***** way of doing modulation? I can't quite work out how allowing/forcing more/less air into the boiler would make it modulate, this would just change fuel/air mix and make combustion less efficient which would have the effect of less heat to the exchanger but not actually use less gas.

Unless i'm missing something....

Cheers, Nick

 

[Joe4542]

Something to bear in mind then; if it uses a diverter valve then don't they have a mid position when both CH and DHW are calling for heat? What would it do then?

It cant do mid-pos - since boiler can only output at a set temp, and as WC no-where near hot enough for HW cyl, the normal method would be to set cyl to heat before heating is req'd in morning. Then boiler modulates back down and diverter switches back to the CH.The boiler has two inputs for demand, 1 for CH and 1 for DHW - this was it can adjust output temp accordingly, and like Combi's DHW always takes priority.

Sounds logical too about HW because if modulated to lowest setting the water in the system wouldn't be anywhere near 60C I guess.

Yup!

On another note I had been recommended a Baxi 28HE system boiler which apparently "on most models this [is] done by varying the fan speed which will increase /decrease the gas rate as it speeds up and slows down". Does this sound reasonable? Is this just a really ***** way of doing modulation? I can't quite work out how allowing/forcing more/less air into the boiler would make it modulate, this would just change fuel/air mix and make combustion less efficient which would have the effect of less heat to the exchanger but not actually use less gas.

Unless i'm missing something....

Cheers, Nick

No thats the normal method on modern premix type boilers, since the gas rate is directly linked to the fan speed. The faster the fan goes - the more gas is sucked into mix due to a venturi effect. The fuel/air mix doesn't necessarily change (largely).

 

[mickyg]

For what you seem to be trying to achieve you'd be best off with a 4 pipe system boiler such as an ATAG Q or a Viessmann 200. These boilers are built for the situation your trying to achieve.

 

[D_Hailsham]

Remeha use a diverter valve the "wrong" way round, so the heating circuit is the normally open one.

Something to bear in mind then; if it uses a diverter valve then don't they have a mid position when both CH and DHW are calling for heat? What would it do then?

I said a diverter (V4044)valve not a mid-position (V4073). I know many people refer to the mid-position as a diverter, but they are incorrect. The diverter can have either port A or Port B open, not both at the same time.