Ideal Vogue combi. Range rating, or the lack of ......

[Notch7]

Yes, pump runs during anti-cycle to stop overheating in the heat exchanger. Wider delta T is more difficult to acheive as the boiler modulates flow temperature as the 'headroom' reduces. A slower pump would help but it wouldn't be much difference to fuel costs.

That’s very helpful, many thanks for the advice.

It’s not easy for a lay person to know what’s going on with how the electronics is designed and the parameters that determine what it does.

 

[Mr.B]

That’s very helpful, many thanks for the advice.

It’s not easy for a lay person to know what’s going on with how the electronics is designed and the parameters that determine what it does.

I'll second that

 

[Johntheo5]

Its fairly basic, gas boilers can't really deal with very low flow temperatures once the heat demand is less than the boiler's minimum output as they fire up at ~65% of max output and will exceed the target flowtemp by 5C = burner trip and recycle, then, after the recycle time has elapsed and they refire, the flow temp will again exceed targrttrmp+5C before they can modulate down, more anti cycling. Reducing the flowrate will increase the dT but the rad(s) output will then be even less and even worse making it yet more difficult to successfully refire as the boiler requires as high a flowrate as possible to refire.

 

[MNW67]

Assuming dT at almost full output is 15C then you just can't avoid running at a dT of 5C or less with WC once the flow temperature is less than ~ 40C, it goes down to 3.7C with a flow temperature of 37C don't know what the minimum output of your boiler is but just assuming 6kw then the rated outout of your rads must be ~ 6/0.23, 26kw to avoid the boiler cycling and its going to be very difficult for it to fire up without repeated cycling at a flow temperature of 36C.

Thanks. That's so interesting. I'd really like to see the same calculation but starting with a dT of 20C at a flow temperature of 60C?

 

[Johntheo5]

Thanks. That's so interesting. I'd really like to see the same calculation but starting with a dT of 20C at a flow temperature of 60C?

 

[MNW67]

gas boilers can't really deal with very low flow temperatures once the heat demand is less than the boiler's minimum output as they fire up at ~65% of max output

That's not true of all boilers. Some start at approx 65% of the range rated value and then ramp up slowly. Intergas, Alpha and newer Vokera definitely do this. Extending the anti cycle time gives further headroom. Other boilers, as you say, come on at ~65% of max and can't be range rated, so they give it the full bananas until they get close to Set Point.

 

[Johntheo5]

That would be fantastic but I'm a little skeptical.
Vaillnts can certainly be range rated but still fire up at 65% or more of their rated output, the older ones used then (don't know about their latest offerings) maintain this firing rate for up to 60 secs before allowing modulation.

 

[Notch7]

Assuming dT at almost full output is 15C then you just can't avoid running at a dT of 5C or less with WC once the flow temperature is less than ~ 40C, it goes down to 3.7C with a flow temperature of 37C don't know what the minimum output of your boiler is but just assuming 6kw then the rated outout of your rads must be ~ 6/0.23, 26kw to avoid the boiler cycling and its going to be very difficult for it to fire up without repeated cycling at a flow temperature of 36C.


View attachment 336473

Thank you very much, that’s really useful

I’m in the process of doing a garage conversion which will add to rads to the system, I guess that will help extract more heat out of the system thus increasing dT.

There’s currently no radiator in the kitchen, I had planned to put in a hydronic plinth heater, but I’m slightly wondering if it will work in a system with low flow temps

I believe the min Ideal vogue CH output at 40 deg is 3.9kw

 

[Mr.B]

I believe the min Ideal vogue CH output at 40 deg is 3.9kw

Off the top of my head that figure relates to the lower sized Vogue. The 32kw combi that I've been looking at is higher. I did quote the figures for the combis somewhere earlier in the thread.

Here is what I wrote earlier ....The Vogue turns down to either 4.6 @ 70 degress (or 4.9 @ 40 degrees.) and that would have been the 32kw.

 

[MNW67]

That would be fantastic but I'm a little skeptical.
Vaillnts can certainly be range rated but still fire up at 65% or more of their rated output, the older ones used then (don't know about their latest offerings) maintain this firing rate for up to 60 secs before allowing modulation.

I am sure that vulcancontinental has said before that newer Vokeras start at ~65% of range rated output then ramp up over the next 15 minutes to the full range rated output.

Alpha seem to do something similar according to the manual.

Intergas have step modulation

Step modulation is set to function (factory setting) so that the power/speed is increased gradually from the minimum (parameter c). This provides the best CH operation.

 

[Johntheo5]

Off the top of my head that figure relates to the lower sized Vogue. The 32kw combi that I've been looking at is higher. I did quote the figures for the combis somewhere earlier in the thread.

Here is what I wrote earlier ....The Vogue turns down to either 4.6 @ 70 degress (or 4.9 @ 40 degrees.) and that would have been the 32kw.

Anyone who's interested can do their own calcs below, I had to .zip my file to post it. Just change the values in yellow.

 

[Johntheo5]

I am sure that vulcancontinental has said before that newer Vokeras start at ~65% of range rated output then ramp up over the next 15 minutes to the full range rated output.

Alpha seem to do something similar according to the manual.

View attachment 336515

Intergas have step modulation

This is what it states in my daughter's 9 year old Vokera Vision 20S MIs.
Not sure how to interpret it but it certainly comes up to target temp very rapidly but the heating load is only ~ 12kw max, but I allways thought that it would take 15 minutes to incrementally rise from 75% to 100% if target temp not reached in the meantime.

 

[MNW67]

This is what it states in my daughter's 9 year old Vokera Vision 20S MIs.
Not sure how to interpret it but it certainly comes up to target temp very rapidly but the heating load is only ~ 12kw max, but I allways thought that it would take 15 minutes to incrementally rise from 75% to 100% if target temp not reached in the meantime.

I'm quoting a two year old post below. It seems categorical that the 75% mentioned is 75% of the range rated maximum. I imagine we would have an ignition sequence (3 or 4 seconds?) at perhaps 50% of full output, followed by maybe 10 seconds also at that output to check the flame is stable. Then the boiler drops to 75% of range rated output, then gradually ramps up. As regards some other manufacturers, this info is not easy to get hold of. I have no idea how Worcester Bosch and Ideal do it.

Vokera not only limit htg output to 75% for the first 15 minutes but the limit is 75% of the range rated heating output not the maximum htg output.

 

[gas112]

I note you’ve not helped the OP by stating the problem has been corrected and a new boiler won’t suffer that problem.

Please can you quantify “loads” That could mean half a dozen.

How do you know Ideal are telling their staff to,”down play it”


Perhaps you should try sticking to facts

There is still hundreds out there in merchants and people`s personal stock (many people bought loads of boilers before ist of jan to beat the 150 quid increase) that could still be getting fitted for months to come only this week my two local plumbcentres sent 30 back to ideal that they had on the shelf still . So no there is no absolute certainty the new boiler wont be known as a faulty one till its registered with ideal
And because we are in the trade and in contact with reps on a personal level who speak to us
As i have said stop commenting on something you know fek all about

 

[Notch7]

So no there is no absolute certainty the new boiler wont be known as a faulty one till its registered with ideal

Here’s a tip for you gas: ring Ideal and get them to check the serial number before installing.

Perhaps you didn’t know that every gas boiler has a unique serial number.

Glad to be able to help, is there anything else I can help with?