Evohome Query

[colin_]

Hi

I would appreciate a reply from someone who has an Evohome system fitted please.

When the system is near its set point (but not over it yet) then the Evohome appears to restrict the HR92 on the radiator down and call for heat from the boiler (default on time of 1 minute in every 10).

Now 1 minute is not long for the boiler to get up to temperature (I have mine at 3 minutes as slow start up from low modulation) and so, when in this mode and 1 minute boiler starts, do your radiators feel hot (at say 70 degrees) or are they just "slightly warm" near the top of the radiator (as system thinks it only needs a small boost and so hardly anyheat differentail required).

Thanks
Colin

 

[Basher]

I do have Evohome with HR91's in 9 zones (more to be added), system boiler, y-plan, etc.
I have been following your adventures with short cycling!
We have never noticed the issue you've previously described, and I was unaware of some of the quirks of Evohome that you've uncovered.

You mention 'set point' in relation to the system, but in our case we have set different temperatures in different rooms, and these are different for different times of the day.
So taking an example room, when first heating from cold radiators go to max temp, say 60 deg or whatever.
As the room temperature approaches the set point, the valve throttles the flow and the radiators cool.
During the period the room is maintaining its set temp, the radiators reduce dramatically in temp to the point, in this weather, they feel cool, or maybe even cold, but the temperature on the Evohome display shows the steady set temp, say 21deg, or whatever is set. The actual temperature in the room tracks that.

At present our boiler typically runs for a few minutes every 15 to 30 mins pumping water at 60deg round the system, but radiators at set temperature are cool or lukewarm to the touch.

Our house is not well insulated, so in the really cold weather, the radiators are a lot hotter to the touch when maintaining set temperature, even to the point of not being able to keep your hand on them. But right now our rads are barely warm to maintain set temp.

Not sure if any of this will help. We are happy with Evohome, and our heating has been much more effective with it, compared to the basic TRV's we had previously.

 

[colin_]

I do have Evohome with HR91's in 9 zones (more to be added), system boiler, y-plan, etc.
I have been following your adventures with short cycling!
We have never noticed the issue you've previously described, and I was unaware of some of the quirks of Evohome that you've uncovered.

You mention 'set point' in relation to the system, but in our case we have set different temperatures in different rooms, and these are different for different times of the day.
So taking an example room, when first heating from cold radiators go to max temp, say 60 deg or whatever.
As the room temperature approaches the set point, the valve throttles the flow and the radiators cool.
During the period the room is maintaining its set temp, the radiators reduce dramatically in temp to the point, in this weather, they feel cool, or maybe even cold, but the temperature on the Evohome display shows the steady set temp, say 21deg, or whatever is set. The actual temperature in the room tracks that.

At present our boiler typically runs for a few minutes every 15 to 30 mins pumping water at 60deg round the system, but radiators at set temperature are cool or lukewarm to the touch.

Our house is not well insulated, so in the really cold weather, the radiators are a lot hotter to the touch when maintaining set temperature, even to the point of not being able to keep your hand on them. But right now our rads are barely warm to maintain set temp.

Not sure if any of this will help. We are happy with Evohome, and our heating has been much more effective with it, compared to the basic TRV's we had previously.

Hi

I have many set points in the different rooms and if far away from the set point the Evohome puts boiler on fully for 10 minutes so boiler has time to get to 60/70 degrees and the radiators feel hot.

When near/maintaing temperature the issue I had was that the radiators never got past cold. So far I have had to set my minumim on time to 3 minutes and set the boiler min modulation to 20% otherwise by the end of the "on" time the water has not moved from ~30 degrees to 37 degrees, now it will, eventaully after many 10 minites cycles get the boiler to around 45-50 degrees but never higher (and eventaully register no demand after ~30 mins - 1 hour of cycling the boiler) but the radiators will be cooler as that has to get around all the throttled valves.

I notice the cycling as I am directly above the boiler and drives me mad!

If its no trouble could you please let me know, when your system is topping it up for the minute or so what the boiler temperature output says and whether during that time the radiators go hot or not (mine get slightly warmer at the top but never more than luke warm during that period).

Resideo say it takes 2-3 weeks to learn each room and that it should have done so by now, but as someone has mentioned before, it can only learn when it actually moving the zone valves (which requires it to be colder as it is/was now getting).

Thanks
Colin

 

[Basher]

Hi Colin
On demand our boiler (Intergas 40SB) ramps up straight away to near full power (dependant on delta T), apparently unlike yours.
Approx 30 minutes ago, our boiler ran for 5 minutes (60 deg flow, 50 deg return). Right now it's still off, pump off, and the flow is 52 deg and return 42 deg.
In the meatime I haven't really noticed any significant change in the touch temperature of the radiators. Those that were warm still feel warm!
Ours is a biggish house, and I think our system has quite a 'thermal inertia', whatever the technical term is, so after it heats up first thing, it seems to 'freewheel' with periodic infrequent topping up from the boiler.

There are of course loads of pump and boiler parameters in play (I'm no expert), compounded by there being no serious demand for heat at the moment(?!), so I hope your issue will settle down. Do you have access to an experienced engineer who could advise on boiler settings (there are 30+ different adjustable parameters on ours!)

 

[John.g]

What's your minimum run time set to and the cycles per hour.

 

[colin_]

Hi

Thanks for all the replies

I think the slow start function of the Worcester is part of the issue I have. I have set it for 20% modulation but even after 3 minutes it has barely got the temperature up from 30 at start of on and 45-50 at the end of the 3 minutes.

I have tried setting more power and longer times but while it did get to temperature the boiler then started turning off the burner after around 45 seconds (presumably as the heat was not being removed fast enough) and so have decided for now to

minimum runtime at 3 minutes
6 cycles per hour
min boiler modulation 20 % (=> 30KW a 0.2 => 6KW)

and see if the Evohome learns to let it be on for longer by itself as it starts to have more colder periods.

Thanks
Colin