Anti Cycling mode on hot water only

[Agile]

It's a big 5 bed house so went for a biggest vailliant do.

We had the system installed about 3 years ago, not sure if any heat loss calcs were done. Who would do that, the heating company?

Well when sizing boilers you don't just "go for the biggest" you rate them for the size of house and its heat loss. Probably needed about 18 kW !

You presumably had a nupty installer too who just did what YOU asked for because you are the customer and ( think ) you know best!

That's why its always better to get a competent installer and take his advice on the specifications!

As suggested set the d0 to 20 and see how that gets on. In fact during the summer I would suggest you set it to 16 which is likely to still be more that would ever be needed except in the coldest weather.

Tony

 

[mrshr]

There are 23 rads, 4 of which are towel rads.

My installer is useless. No point in involving them any further. When I asked about this, I got a shrug of the shoulders and a, "will come back to you on that one."
We all know what that means!!

FWIW this company is listed on the Vaillant website as a Vaillant installer in my area and is also on the Gas Safe Register website. It means nothing really.

I need to look into this d setting you guys are referring to as don't know what it is yet.

From what little reading I've done so far on it, I assume it's some sort of 'governor' that limits the 37kW boiler output to say 20kW?

Like having a Ferrari but limiting it to having a max speed of 70mph???

 

[Dan Robinson]

Why own a Ferrari when you live at the end of a dirt track?


Ultimately though, without careful tweaking of various settings you won'#t eliminate this issue completely, and there is also the question of how short life is.

 

[mrshr]

and there is also the question of how short life is.

Agreed, but my concern is the life of my boiler might be even shorter due to this.

Do you guys like weather compensators? Would that help my situation?
I'm sure I read that the Vaillant weather compensator sets boiler to max temp for heating the cyclinder and then adjusts the temp for the rads, based on outside temp.

 

[Dan Robinson]

In your case I doubt it would be worth it. You would need to install the complete suite of Vaillant controls and as mentioned, these are not compatible with the Megaflow.


If you are going down that route you should have had a Vaillant cylinder installed too.

Although an installer with a good understanding of control wiring might be able to get it to work, at the expense of your cylinder warranty.

 

[mrshr]

Oh ok, I hadn't realised the weather compensator needed a Vaillant cylinder too.
So that's out.

With regards to the d setting thing. Wouldn't that invalidate my warranty if I tinkered with it?
Or are you saying I get an engineer to tinker with it?

 

[Dan Robinson]

If you can get in to change the setting then your warranty is unaffected.

If you can't get in to change the setting then your warranty is unaffected. Just don't go fiddling with other settings.

 

[Agile]

You can reset the d0 and ideally to 16 kW yourself. Plenty of instructions for you to find with a search here.

The gas safe registration only means that he is tested as safe to work on gas.

The Vaillant registration only means that he has been on their course and agrees to fit a lot of their boilers.

NEITHER means that he is technically much good! In fact most who only install boilers know little about the technicalities. Thats the province of those who repair boilers.

Weather compensation is very good if you leave it alone but not if you are a fiddler. But they are not cheap but can save you about 3%-6% on your gas bill.

As far as I know it is possible to get the Megaflo to work reasonably well with the Vaillant controls.

Tony

 

[Agile]

Weather comp does need a mental state willing to accept what it does and not to touch it.

Tony

 

[Dan Robinson]

As far as I know it is possible to get the Megaflo to work reasonably well with the Vaillant controls

Have a quick gander at the megaflow instructions T.

 

[mrshr]

You can reset the d0 and ideally to 16 kW yourself. Plenty of instructions for you to find with a search here.

Are you saying that I drop it down to 16kW during the summer months and then take it back to full speed during the winter or just leave it at 16kW all year round?

The gas safe registration only means that he is tested as safe to work on gas.

The Vaillant registration only means that he has been on their course and agrees to fit a lot of their boilers.

NEITHER means that he is technically much good!

Agreed, 100%

Weather compensation is very good if you leave it alone but not if you are a fiddler. But they are not cheap but can save you about 3%-6% on your gas bill.

Is that all? I thought they were supposed to provide better savings then that as the boiler is mainly operating in condensing mode and not burning gas at full bore.

 

[Dan Robinson]

Not sure why Tony is suggesting 16 to my 20... but changing the setting is primarily to see if the cycling is reduced.

You should lower it to the approximate heat load of the house; whatever that is. Seasons will make flock all difference.

 

[mrshr]

OK so I need to work out the heat load/losses of the house.
Don't suppose that's a straight forward job, is it?


Let's just make sure I've properly explained my problem.

Time clock fires boiler up to heat cylinder. It runs at full pelt (maximum noise) for about 35 mins.
Then:

1) The radiator symbol starts flashing on the boiler display (manual says that's anti cycling mode) and boiler still running but at reduced noise (I think because burner has shut off).
Boiler continues to whirl (at the reduced noise) for about 4 mins. Temp readout on boiler display slowly drops (by about 10 deg) whilst this is occurring.

2) Then boiler shuts off completely. (Total silence)

3) A couple of mins later the boiler fires up and runs at full pelt (max noise). Will run at full pelt for about four mins and then radiator icon starts flashing on the display again, boiler runs at the lower noise level (burner off?) and we're back at stage 1) again.

This repeats until the time clock expires.


Turning the cylinder stat after all this confirms that the stat set point hasn't quite been reached. (I tested this by slowing turning the stat down and listened for the click).

Not sure if my this explanation changes anything of your understanding of the situation, or perhaps you understood it well enough from my first post?

I guess if stage 2) didn't occur I'd probably be ok with it. i.e. if the boiler didn't completely shut off for a few mins and then fire up again. It's that short on/off cycling of the boiler that's worrying me.

 

[Dan Robinson]

I would just bang d.0 down to the levels we have discussed and see if that helps.

 

[picasso]

If that does not work go into d2 and set the anticycle at 60 minutes, that will stop the boiler firing for around 7 minutes (if the flow temp is set at 70c)