What is considered to be short cycling

[Johnnyt]

I’ve found a menu on my system boiler that shows since commissioning last October, the burner has been on for 2078 hours with burner starts of 6201.

It feeds ufh with no buffer and 500l UVC .So it cycles circa every 20 mins on average.

Is this good bad or indifferent?

[RobLe]

For a heatpump thats considered just ok, 3x an hour.  The restarts shock the system, fatigue the brazed joints, reduce its life.  

[JohnMo]

With all boiler types you get a big drop in efficiency, every time you go through a start cycle as all the metal parts soak away the heat during the heat stabilisation phase.

 

Reduce zones as much as possible, no small zones, try to reduce central heating flow temperature so boiler has to run for longer.  Low and slow, is the way to go.

[SimonD]

I reckon you need to check the configuration of the system. Has it been installed for priority domestic hot water? If you're going to run lower flow temps on the ufh you'd be much better of with this setup. PDHW means that the boiler runs at two difference flow temperatures - a high temperature for your uvc to get to temperature quickly and a lower, variable temp, ideally modulating/weather compensating for the heating system. Also look at the balancing of the system - what's the flow and return temperature across your heating system? Unfortunately not a lot of installers understand this this stuff let alone set the system up properly to do this ☹️ Without the separate temps, you rely on the same flow temp to heat both your uvc and heating system which can lead to this kind of problem.

Edited August 12, 2022 by SimonD

[Johnnyt]

It was piped as a 2 pipe system but was changed to 4 pipe in February after I dicussed this with the plumber.

The DHW has priority and shuts of the UFH circ when hot water is called for.

So the figures could be skewed by the pre Feb cycling.

I have set a flow temp of 48c 8am to 7pm and 40c 7pm to 8am

I will check this winter how it goes.

It's a viessman 200 25kW, I have seen it modulate down to  to 2.25kW

[JohnMo]

If it's UFH, why are your flow rates to high?  Seem high temps.

[Johnnyt]

I guess because it’s blended down at the mixer to about 35, I think.

I can reduce my flow temps and have three different flow temp profiles a day.

Would it be better to go lower?

[PeterW]

That’s not condensing. Up the DHW flow temp to 62°C and hold it for longer. 

[JohnMo]

Confused, what's not condensing? Condensing with natural gas starts with a return temp of 54 degC and lower.  The lower the return temp the more condensing that occurs.  The more efficient the boiler becomes.

 

With UFH there is no point heating water up, to then mix it down to a cooler temp.

[Johnnyt]

I have the DHW flow temp set to 55c

And the UFH flow temp at 48 and 40.

This winter I'll reduce my UFH flow temp to say 40 all day and see what happens re cycling.

I can then reduce it each week by say 1 or 2 c and see what happens.

As an aside I don't have weather comp.

I do think this is low but I am on here to learn.

[JohnMo]

Your boiler has weather comp built-in.  Go on to heat geek website and have a read up on weather comp.

[PeterW]

1 hour ago, JohnMo said:

Confused, what's not condensing? Condensing with natural gas starts with a return temp of 54 degC and lower.  The lower the return temp the more condensing that occurs.  The more efficient the boiler becomes.

 

With UFH there is no point heating water up, to then mix it down to a cooler temp.

Not talking about the UFH - sorry ! The DHW needs to be higher - you’ll lose 10-15°C min on the full burn cycles so at 62°C you’ll get into  the 47°C sweet spot especially with a 500 litre UVC. I would run that with two long blocks though and not be constantly pulsing into it. 
 

UFH and gas needs a buffer - anywhere to fit one ..?

[Johnnyt]

16 hours ago, PeterW said:

Not talking about the UFH - sorry ! The DHW needs to be higher - you’ll lose 10-15°C min on the full burn cycles so at 62°C you’ll get into  the 47°C sweet spot especially with a 500 litre UVC. I would run that with two long blocks though and not be constantly pulsing into it. 
 

UFH and gas needs a buffer - anywhere to fit one ..?

 

Yes I have, the flow and return to the manfold  and pump pass through a void which is accessible.

About 8 ft above manifold approx a meter square with a height of about 4ft.

[Onoff]

The corner shop and back?

[Johnnyt]

1 hour ago, Onoff said:

The corner shop and back?

 

'appen

[Ferdinand]

Are we allowed to be semi-satirical?

 

 

(Or am I in trouble again?)

[Johnnyt]

Will it fit on my mousetrap?

[Ferdinand]

20 minutes ago, Johnnyt said:

Will it fit on my mousetrap?

 

Depends what you have been drinking 😁

 

 

(Soda Water, since you didn't ask. I'm an Orangina man. )

 

Try getting that past the Advertising Self-Appointed Authority.

[Johnnyt]

I'd a gallon but my local only serves Tetleys!