Has anyone had any success in preventing their boiler from short cycling?

danlightbulb said:
Boilers turn off if the return temp is too close to flow temp or if the stat tells it to.

If the rads are actually hot (are they very hot or just warm?) then they still should be dissipating heat into the room.

You say you upped the flow temp setting, has this helped or not?
Click to expand...

It's weird because I spent ages balancing them, even though they're ****. So the return temperature is relatively low - as low as you're likely to get it without having better kit.

I made a few changes so I don't know whether changing the flow temp helped. I will check tomorrow.

Hyburnate said:
Unless I'm completely missing something you have ambient temp and target temp.

Ignoring opentherm etc etc

If it's 16 and you want it to be 21, your boiler is sending heat out at the flow temp until the thermostat hits 21 and then it stops sending heat.

Where is your thermostat? Is it in the coldest room?
Click to expand...

Thermostat is in the same room where I'm monitoring the temperature.

jpaul said:
following other current thread on boilers - this boiler modulates 5:1 https://professional.vaillant.co.uk/specifiers/products/ecofit-sustain-25-30-and-35kw-48448.html
so minimum output maybe 5Kw ... and if the house only needs ~3 say, like other thread - it will switch on and off.
eg. on for 6 minutes off for 4
Click to expand...

That's what I set to Automatic, though i'm not sure that I trust it. The installer had set it to 18 kW!

danlightbulb said:
So according to Google there's lots of reasons a boiler could short cycle.

It might be worth getting someone in to service the system OP.
Click to expand...

Yeah I saw that. Quite annoying. I don't really trust plumbers tbh, maybe a heating engineer. It was recently serviced.
 
Last edited:
dirtychinchilla said:
I'm trying to get the temperature up in our house. It's only 2.5 years old, so well-insulated and a modern boiler (Vaillant EcoFit Sustain).

It doesn't seem to be able to actually get the house to temperature, and it's quite annoying. We're preparing for our first child's arrival in the next week or so, so I need it to be warm.

I think what's happening is that the output of the boiler is too high, so it sends heat out, the radiators can't give it off in time, and it somehow ends with the boiler short cycling.

I have adjusted the settings to set the output to "Auto" which apparently matches output to system demand, but the temperature in the house has only very slowly been creeping up.

Any ideas?!
Click to expand...

Boiler stuff aside, your room doesn't need to be a furnace for your newborn. With 3 of you sleeping in the room it'll naturally be a bit warmer. Do you have any temperature sensors/thermometers in the room to actually gauge the temperature?
 
Semple said:
Boiler stuff aside, your room doesn't need to be a furnace for your newborn. With 3 of you sleeping in the room it'll naturally be a bit warmer. Do you have any temperature sensors/thermometers in the room to actually gauge the temperature?
Click to expand...

I agree. It's the living room I'm trying to sort out really. We've got a couple of those egg things - one for the living room and one for the bedroom.
 
Last edited:
dirtychinchilla said:
I don't think that would cause it to short cycle. I think it may work if I set the output to something like 5 kW.
Click to expand...
I think root cause of short cycle will be return flow temp is too high and it stops firing.
dirtychinchilla said:
Currently 70 as we're at peak low temp. It's usually 55
Click to expand...
That's way too high for a new build. I have a 50 flow temp on my 1930s semi and it is never cold. Your rads won't be big enough to spit out 70 degrees before returning hot water to the boiler.
 
Last edited:
dlockers said:
I think root cause of short cycle will be return flow temp is too high and it stops firing.

That's way too high for a new build. I have a 50 flow temp on my 1930s semi and it is never cold. Your rads won't be big enough to spit out 70 degrees before returning hot water to the boiler.
Click to expand...

You might be right. As I said, I do manual weather comp, but I don't think that's the route cause of the problem. I'll try a couple of things.
 
I don't know if I'm being dense here either, but I can't work out what to set the anti-cycling time to. Maybe because I'm not a heating engineer.

ZWiGJHM.png
 
What you currently set at, must be a few mins? allowing it to fire back up again. Up that and your pump will continue to pump the hot water around, rejecting the heat, but boiler won't fire and cycle.
 
rodders said:
What you currently set at, must be a few mins? allowing it to fire back up again. Up that and your pump will continue to pump the hot water around, rejecting the heat, but boiler won't fire and cycle.
Click to expand...

I set it to 15 mins and that may well have improve things.

Maybe it’s all three: reduce the flow temp, limit the capacity, and up the cycle time (or leave it at 15 mins).
 
Ours was short cycling but it's a different scenario to yours. Ours is an oil fired boiler which doesn't modulate, it's either on or off.

Balancing the system and getting your return to be lower will help, I find a lot of TRVs have poor valve authority/flow isn't really restricted until the valve is barely open.

For us, balancing the system, switching the pump to proportionate pressure mode and getting the output turned down to minimum has helped.

Like dlockers said, a lower flow rate might help - you'll get up to temperature slower vs what seems to be happening now which is the boiler is dumping so much heat out and it's bouncing off the stat inside the boiler. Although I don't know how this can be happening with such a modern combi boiler considering they can modulate down.
 
dirtychinchilla said:
I set it to 15 mins and that may well have improve things.

Maybe it’s all three: reduce the flow temp, limit the capacity, and up the cycle time (or leave it at 15 mins).
Click to expand...
Is the cycle time the minimum on time?
I haven't really looked at mine I kind of let Evohome do it's thing.
I have Min on time, and max cycles and hour.
 
What is your return temperature at the appliance? If the temperature difference between flow and return is to big it can go into S53. I would set the KW output manually start at 12 and work your way up.
 
@dirtychinchilla When you say your boiler is short-cycling, do you mean it's going fully off (as in, stops firing and stops the pump and fan completely) or just the flame is kicking in and out whenever heating is called for?

What thermostat do you have controlling the boiler?
 
You must log in or register to reply here.
Back
Top Bottom