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Hi All,
The house we moved in to a year ago has a Vaillant Ecotec 428 fitted and I'm trying to get my head around how it works. This is my first time as a home owner and never lived in a property in which I've had access to the boiler until now, so trying to get my knowledge to where it should be!

The boiler runs through a UPS 15-60 pump and 3x CH zones (one of which is UFH with a separate UPS 25-60) plus the HW cylinder. I have the boiler HW temp set to 60 deg and the CH temp set to 75 deg (as I'm pretty sure was recommended in the manual or elsewhere). What is confusing me a little is the way the boiler is reacting in relation to the set temps.
The weather has (thankfully) been glorious as of late so the CH heating has been off (ie set low enough through our Tado that there is never any call for heat) yet when the Hortsman progammer (which all the Tado thermostats run through) has the HW channel ON in the morning and evening the boiler LCD displays both the radiator symbol (heating mode) and the tap (hot water supply). Why is the heating mode active when there is no call for heat from the CH side of the system?
What's more, when the HW is on, the boiler constantly goes through short cycles of heating up (heating mode) to 75 deg probably takes about 30 seconds with all the CH zone valves closed, flame turning off, heating then entering an anti-cycling mode (flashing radiator) until it gets down to around 70 deg (probably take 2 minutes) before repeating. Why is the boiler heating to the CH temp with no call for heat? Why is it not just maintaining the HW temperature? Should it he cycling on and off so short and repeatedly?

Thanks in advance for any help/advice you can provide!
 
It’s possible that one of your zone valves has a stuck microswitch or a burnt out sychron motor. Do any radiators heat up when the hot water is on? Does this happen with no demands?
 
It’s possible that one of your zone valves has a stuck microswitch or a burnt out sychron motor. Do any radiators heat up when the hot water is on? Does this happen with no demands?

Only radiators that heat up without demand are the heated towel rails upstairs but they branch off before the valves to always provide a flow from what I can tell, so to be expected?
When the HW channel isn't ON then the boiler is just idle, so seems to only be an issue when the HW programmer is asking the boiler to be on. In terms of correct operation, am I right in thinking that the radiator symbol should only be on when there is a call for heat from the thermostats and only the HW tap symbol on when the only demand is from the HW channel??
 
It sounds as though you do not have Vaillant controls?
If you have not then the DHW (domestic hot water) control temperature is not relevant. The only temp you can set is the boiler temp. This temp is the same for the DHW coil/cylinder as well as the rads. It will appear as though you can set the DHW temp but you cannot.
The issue with it firing when the valves are closed could be one of a number of things but it doesn't sound right. I would advise you to get a heating engineer in to look at it.
 
It sounds as though you do not have Vaillant controls?
If you have not then the DHW (domestic hot water) control temperature is not relevant. The only temp you can set is the boiler temp. This temp is the same for the DHW coil/cylinder as well as the rads. It will appear as though you can set the DHW temp but you cannot.
The issue with it firing when the valves are closed could be one of a number of things but it doesn't sound right. I would advise you to get a heating engineer in to look at it.
Ah perfect, wondered if that may be the case - I have none of the additional Vaillant controls, so the radiator heating indicator will be on for when the boiler is firing for both CH and DHW. Thanks, very useful bit of info! I will probably turn it down towards 60 then over the summer period when we aren't using the rads.
If think that must mean I effectively don't have an issue with it firing when the valves are closed, in that the programmer will be asking for the hot water cylinder valve to open and for the boiler to fire - I guess the issue is lack of awareness on my behalf that CH rad indicator is in effect the indicator for a call for heat from anywhere within the system, including the DHW?

How about the short burn cycles repeating every few minutes, is that an issue??
 
I may be interpreting this incorrectly but you seem to think that you are controlling the boiler water temperature to obtain your desired CH or HW temperatures?.
You should be able to select (programme) either CH on or HW on or both CH+HW on together or none on. You should then be able to select your desired CH and HW temperatures, with CH you are changing the desired room or rooms temperature room stat(s) temperatures somewhere between say 18C & 25C, the room stat(s) when satisfied will then shut off the appropriate motorized (zone) valve, if all zones are satisfied then the radiator symbol may still remain (if selected) on.
The HW desired temperature is obtained my changing the cylinder water temperature set point temperature and a motorised valve, traditionally this was achieved by having a thermostat (cylinder stat) strapped to the cylinder and you manually changed the setpoint on this stat, the Tado I assume should change this remotely. (Normally set to 60C)
The boiler water temperature may be changed at the boiler panel or maybe with the remote control? and once set is rarely changed.
Re short burn cycles, this can happen in the HW case if the heat emitted by the cylinder coil is less than the minimum modulated output of the boiler, for example if the minimum boiler output is 5kw and the cylinder coil is only emitting say 3kw (especially when the hot water is near its set point) then the boiler will cycle frequently but the biggest problem which seems to be common to most gas fired boilers is that to achieve proper/safe ignition the burner fires up at ~ 75% output and by the time it has modulated down to minimum the boiler temperature has exceed its setpoint by ~ 5C and cuts out the burner which then has to complete a anti rapid fast cycle time of maybe 2 to 5 minutes before it refires on reaching its SP temperature.
 
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I may be interpreting this incorrectly but you seem to think that you are controlling the boiler water temperature to obtain your desired CH or HW temperatures?.
You should be able to select (programme) either CH on or HW on or both CH+HW on together or none on. You should then be able to select your desired CH and HW temperatures, with CH you are changing the desired room or rooms temperature room stat(s) temperatures somewhere between say 18C & 25C, the room stat(s) when satisfied will then shut off the appropriate motorized (zone) valve, if all zones are satisfied then the radiator symbol may still remain (if selected) on.
The HW desired temperature is obtained my changing the cylinder water temperature set point temperature and a motorised valve, traditionally this was achieved by having a thermostat (cylinder stat) strapped to the cylinder and you manually changed the setpoint on this stat, the Tado I assume should change this remotely.
The boiler water temperature may be changed at the boiler panel or maybe with the remote control? and once set is rarely changed.
Re short burn cycles, this can happen in the HW case if the heat emitted by the cylinder coil is less than the minimum modulated output of the boiler, for example if the minimum boiler output is 5kw and the cylinder coil is only emitting say 3kw (especially when the hot water is near its set point) then the boiler will cycle frequently but the biggest problem which seems to be common to most gas fired boilers is that to achieve proper/safe ignition the burner fires up at ~ 75% output and by the time it has modulated down to minimum the boiler temperature has exceed its setpoint by ~ 5C and cuts out the burner which then has to complete a anti rapid fast cycle time of maybe 2 to 5 minutes before it refires on reaching its SP temperature.
Thanks for your reply John, I'm not 100% clear what you mean however. My understanding now from the earlier post from Last Plumber is that although I have separate CH and DHW rotary temperature setting knobs on the front of my specific boiler, the DHW one is redundant without the additional vaillant controls (I see where it suggests this in the manual now) so the CH knob is in effect setting the boiler temp (outflow?) for the whole boiler, regardless of if the call for heat is generated by the DHW via the cylinder/programmer or the Tado thermostats that control the rads. Is that correct? Obviously the actual room/cylinder temps are controlled by their individual settings, with radiators heating up quicker and hotter (so end call for heat quicker) with a setting of 75 deg on the boiler compared to if I set a lower temp like 60 deg.
My logic behind setting the boiler temp down to 60 deg over summer is that I don't need the rads to heat up quickly (or indeed at all) and 60 deg should be plenty to get the water temp up to a decent amount without wasting too much energy - or is that logic flawed in that it will take a set number of KW to warm up the hot water cylinder no matter what the temp is set at, all it will change is the speed at which it warms up?
As to your second point, I think that is what my problem is. Someone elsewhere has suggested I de-rate the boiler down from 28 kw as that is very excessive for what the two of us need for how we use the house (we don't yet have the three kids the previous owners had!) - would that help with the short/micro cycles or will the boiler always start up at 75% of max output and ignore the derated output?
Unfortunately I haven't yet found an electrician who is interested in wiring up the HW to the Tado, so that, rather annoyingly, is still controlled by a white thermostat on the side of the cylinder as far as I'm aware - I've not touched it since we moved in!
 
Setting the boiler temp to 60C should improve its efficiency by a few % but because the hot water should be kept at 60C (legionella protection) then the boiler should be set ~ 10c higher otherwise it will never reach its setpoint. Some boilers can be configured with a outside temperature sensor and depending on outside temperature can lower the boiler water temperature to 40C or so which gives greater efficiency but this gain will be reduced if the boiler is cycling, when HW is required the boiler SP is automatically increased while there is this demand.
Thermostatic rad valves do improve boiler efficiency by lowering the return temperature to the boiler so one could still have a relatively high boiler temp of 75C and if the rads are adequately (over) sized then very low boiler return temps can be achieved.

De rating still requires the same start up conditions as far as I know, there has been numerous posts on here re this short cycling, but as a lot of boilers only have a modulation ratio of ~ 5:1 then this doesn't meet the very low energy demands with zoning and high levels of house insulation. I think there are boilers now appearing that can go below 2kw output and I think Vokera had/has a boiler with a 10:1 ratio.
 
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Setting the boiler temp to 60C should improve its efficiency by a few % but because the hot water should be kept at 60C (legionella protection) then the boiler should be set ~ 10c higher otherwise it will never reach its setpoint. Some boilers can be configured with a outside temperature sensor and depending on outside temperature can lower the boiler water temperature to 40C or so which gives greater efficiency but this gain will be reduced if the boiler is cycling, when HW is required the boiler SP is automatically increased while there is this demand.
Thermostatic rad valves do improve boiler efficiency by lowering the return temperature to the boiler so one could still have a relatively high boiler temp of 75C and if the rads are adequately (over) sized then very low boiler return temps can be achieved.

De rating still requires the same start up conditions as far as I know, there has been numerous posts on here re this short cycling, but as a lot of boilers only have a modulation ratio of ~ 5:1 then this doesn't meet the very low energy demands with zoning and high levels of house insulation. I think there are boilers now appearing that can go below 2kw output and I think Vokera had/has a boiler with a 10:1 ratio.
Thanks kindly John, I will set the boiler temp to ~70 deg and keep an eye on it to make sure the cylinder gets up to temp (>60 deg) easy enough. I'll work out how to de-rate the boiler too, as apparently the 400 series Ecotecs are known to be pretty slow at automatically modulating down but better when de-rated. I see the Viesmann 200-W has a 30kw output but can modulate down to 1.9 KW which is pretty impressive - will have to consider one of those if our current boiler decides to die any time soon!

Another job on the list for this weekend is to look at changing the auto bypass valve as the one in it vibrates and makes a horrendous noise when the zones valves have closed down and the pump is just providing the cylinder. Not fun to wake up to every morning! Will see if that does the trick and if not, consider an Alpha 3 variable output pump?
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Will see if that does the trick and if not, consider an Alpha 3 variable output pump?
On second thoughts, having seen some of the enormous discussions about automatic variable output pumps and auto bypass valves, I might stay well away!
 
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Had the same start/stop cycling and slow system warm-up problem with my ecotec 428.

You've probably got a boiler that's too powerful for the house/installation.

The boiler is putting out 28 kW and the pump/pipework is not able to shift the heat into the radiators/cylinder fast. enough. This is made worse if you've got a high resistance system with microbore to the rads.

The solution was simple on my installation - just turned down/de-rated/modulated the boiler output from the default 28 kW - it only takes a couple of minutes. Turning down the output reduces the fan speed so there's much less start/stop , reduced wear and tear and noise.

Using the diagnostic control panel turn down the boiler output from 28 to say 15kW - 15kW has proved to be fine for my 4 bed detached even in the middle of winter.

See section 10.1.2 of the guide, it tells you how to do it. Manuals available from FREE BOILER MANUALS - https://www.freeboilermanuals.com/vaillant/

The d.0 code is the one to change, it indicates the boiler output (will be indicating 28) - see the description about using the "i" and "+" .

Many heating engineers don't realise that the boiler outputs can be turned down/de-rated.
 
Had the same start/stop cycling and slow system warm-up problem with my ecotec 428.

You've probably got a boiler that's too powerful for the house/installation.

The boiler is putting out 28 kW and the pump/pipework is not able to shift the heat into the radiators/cylinder fast. enough. This is made worse if you've got a high resistance system with microbore to the rads.

The solution was simple on my installation - just turned down/de-rated/modulated the boiler output from the default 28 kW - it only takes a couple of minutes. Turning down the output reduces the fan speed so there's much less start/stop , reduced wear and tear and noise.

Using the diagnostic control panel turn down the boiler output from 28 to say 15kW - 15kW has proved to be fine for my 4 bed detached even in the middle of winter.

See section 10.1.2 of the guide, it tells you how to do it. Manuals available from FREE BOILER MANUALS - https://www.freeboilermanuals.com/vaillant/

The d.0 code is the one to change, it indicates the boiler output (will be indicating 28) - see the description about using the "i" and "+" .

Many heating engineers don't realise that the boiler outputs can be turned down/de-rated.
Thanks Richard, already had de-rate the boiler on the list of things to do this weekend but was looking for info on how to do it, so this is timely.
Agree that the boiler is definitely too big for how we use the house at present, but with 3 bathrooms, a large kitchen/diner with underfloor heating and some good sized living areas I suspect it was probably about right for the previous family of 5 odd. De-rating is definitely the way ahead and if we have to replace the boiler in the future (currently about 12 years old) then one that modulates down to a decent amount will be key.
Some of the plumbing and maintenance of the property left much to be desired (as evidenced by the toilet that was leaking into the ceiling below!) so now just need to get up to speed with understanding how it all should work and then adjusting it as much as I safely can. Our next boiler service is due in Nov, so will try habe it all nicely re-balanced by then so he can give his thoughts about it all.
 
Re ABV with HW circuit ony in use, the ABV shut be fully closed, if its partially open then this won't help the rapid cycling, a few things you can easily check, see if there is a (balancing) gate valve fitted on the cylinder coil return and see how many turns it is open, if this is throttled in too much then the coil will not release much heat also check the ABV setting index, you can read it off the valve itself, it should have a range of 0.1 to 0.5 (bar) or maybe 1 to 5 (M)
 
Managed to get home last night (work away most of the week) and have now de-rated the boiler to 18 KW. Slower time I'll use one of the online calculators to work out a more accurate estimate of our max and normal combine heating and DHW output.
I've also had a chance to test the thermostat on the cylinder and the boilers response to it and all is good - turn the thermostat right down and call for heat and boiler stop - turn it up above the click and the boiler fires up and pumps hot water around it.
What doesn't appear to work though is the ABV - even with the pump on lowest setting and the ABV wound all the way in to 0.5/5 it opens up and let's hot water through. Suspect that might mean it is stuck open? Would the potentially contribute to the awful noise it makes when the pump is turned up any higher than two without multiple zones open?
 
Managed to get home last night (work away most of the week) and have now de-rated the boiler to 18 KW. Slower time I'll use one of the online calculators to work out a more accurate estimate of our max and normal combine heating and DHW output.
I've also had a chance to test the thermostat on the cylinder and the boilers response to it and all is good - turn the thermostat right down and call for heat and boiler stop - turn it up above the click and the boiler fires up and pumps hot water around it.
What doesn't appear to work though is the ABV - even with the pump on lowest setting and the ABV wound all the way in to 0.5/5 it opens up and let's hot water through. Suspect that might mean it is stuck open? Would the potentially contribute to the awful noise it makes when the pump is turned up any higher than two without multiple zones open?

There definitely seems to be something amiss with that ABV as that UPS pump (if I am looking at the right curve) on speed 2 will only produce a head of 5M at a flow rate of ~ < 0.22 M3/hr (3.7 LPM) and any one zone should circulate more than this keeping the ABV closed.
The pump on speed 1 has a no flow head of ~ 4.6M so again there should be no flow whatsoever through the ABV under any conditions on index 0.5.
There just may be a bit of crap under the seat, you should be able to remove the valve head and inspect/clean it but will probably need system drain down, as this is messy/time consuming you may be better off installing a new ABV.
 
There definitely seems to be something amiss with that ABV as that UPS pump (if I am looking at the right curve) on speed 2 will only produce a head of 5M at a flow rate of ~ < 0.22 M3/hr (3.7 LPM) and any one zone should circulate more than this keeping the ABV closed.
The pump on speed 1 has a no flow head of ~ 4.6M so again there should be no flow whatsoever through the ABV under any conditions on index 0.5.
There just may be a bit of crap under the seat, you should be able to remove the valve head and inspect/clean it but will probably need system drain down, as this is messy/time consuming you may be better off installing a new ABV.
Thanks John, I've got a Caleffi ABV (been generally impressed with the quality of the auto bleeds and pressure regulator of theirs that I've installed) so will have to consider doing that this weekend. Naively hoping that I don't have to drain the system down too much if I close all the TRVs down and as many valves etc as I can but pretty sure I'm gonna end up with most of what's upstairs making it's way down the return! Will be worth it if it stops the horrendous noise!

Thanks for the great help you've been John. Will get some more sentinel 100 and let you know how I get on.
 
Thanks, re problems of setting up ABVs to deal with smart pumps like the alpha3 etc on any other mode other than fixed speed there is a interesting thread on here somewhere (will find it later) on using a (3) or 2 port motorised valve as a ABV, i
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Here is the link
 
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John, we are in business - old ABV off (full of black crud which I suspect was holding it open and spring pressure very weak) and new caleffi ABV on.
Not the most scientific setup, but with the pump on any of the three pump speeds there's no horrendous vibrating pipe noise and with it on 1 I can feel the hot water flowing through the bypass at about 2-2.5m with just the hot water cylinder on, so wound the bypass in a bit to open at 3m.
Will keep an eye on it over the coming week or two but think your help will gives us a much quieter start to the day and save a few quid in having a slightly more efficient boiler setup too!
When it's cold enough to start needing the heating I'll balance the whole system to give me a 15-20 delta too.
Thanks for all your help, you've given me enough knowledge to know roughly how it all works and to be comfortable that the system is working OK for now. Incredibly helpful forum!
 

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