Vaillant echo tech plus 418 short cycling on hot water but OK for central heating. Best recommended settings

[Samsg30]

Hi

I have moved to a different home which has Vaillant Echo tech plus 418 boiler installed with open vented cylinder and a central heating system.
The thermostat on the cylinder is set to 60C and the boiler has two radial dials in front to control the flow temperature, both of which are set to 65C so that it can heat up water to 60C and heat demand should stop.
But boiler is doing short cycling when there's only hot water cylinder needs heating up and no demand for central heating.
I have tried turning the thermostat temperature down from 60C to 55C but making no difference.
Upon going through several posts and documents, I am completely confused as to the correct settings I should have before trying to diagnose the short cycling issue.

Would someone be able to suggest some figures on below questions:
1) What should be the thermostat temperature set at the hot water cylinder at max. (PS: I am OK with 60C to keep legionella bacteria out.
2) What should be the flow temperature settings on the boiler for hot water e.g. +5C to whatever thermostat on cylinder is set to or same as thermostat or lower than the thermostat
3) What is the ideal flow temperature settings on the boiler for central heating
4) Anything obvious I can do to fix the short cycling or is it usual for ecotech plus 418 model to short cycle when water in the cylinder has heated up enough?

In my previous house, I had megaflow and boilder always shutdown as soon as the desired water temperture is reached.

Thanks

 

[Swwils]

The boiler's flow temperature setting typically should be slightly higher than the cylinder's thermostat. This allows the cylinder to reach the desired temperature. In your case, a setting of around 65-70°C could be tried.

Short cycling can occur for several reasons, including an oversized boiler, a blocked flue or vent, low water pressure, or issues with the thermostat itself. It's not typical for the Vaillant EcoTec Plus 418 model to short cycle when the cylinder has reached the desired temperature. If you've adjusted the settings as suggested and the issue persists, it's advisable to contact a heating engineer and only adjust settings if your comfortable doing so.

In your previous house, it seems you had an unvented system, which operates slightly differently to your current system. Unvented systems usually have more precise controls over the hot water temperature, which might explain why you didn't experience short cycling there.

 

[Samsg30]

Short cycling can occur for several reasons, including an oversized boiler, a blocked flue or vent, low water pressure, or issues with the thermostat itself. It's not typical for the Vaillant EcoTec Plus 418 model to short cycle when the cylinder has reached the desired temperature. If you've adjusted the settings as suggested and the issue persists, it's advisable to contact a heating engineer and only adjust settings if your comfortable doing so.

Thanks for your reply and confirming that the flow temperature for HW should be more than the cylinder thermostat so the settings as of now looks correct.
On the short cycling note, given that boiler doesn't do short cycling when CH is on, does that mean issue with oversized boiler, blocked flue or vent, low water pressure can be overruled completely? It's a 3 BR property so doesn't look like boiler is oversize if only HW demand is on?
Are their any settings I could try without damaging the whole setup as such? I already had a heating engineer who drained the whole system, refilled, checked the air vents, bleed the valve etc and couldn't see any reason for the short cycling. He wasn't a vaillant approved engineer though and installs quite a few combi boilers only. The one I am talking about is a system boiler so don't know if there's a knowledge / experience gap for him not able to see the issue.
We are looking to renovate house in 2 years time where more rooms and UFH will be installed which will most likely result in replacing the existing boiler anyways.
So my question is, does this everyday short cycling on heating the HW will damage the boiler than can shorten its life to not run for next 2 years and / or causes so much of extra cost in gas bill that can go beyond the calling of heating engineer and paying few £00s which may / may not fix the issue or result in quite a bit of an expense in replacing / fixing any associated plumbing.
Water in the cylinder is getting hot anyways so not causing the daily living quality issues as such.
If some DIY quick tips can work a wonder, I am happy to try those. I am not completely novice either so can try making sense of things

 

[Mottie]

In summertime when I’m only using the boiler for hot water, I have my 418 EcoTEC plus boiler set to a max output of 12kw, flow temperature set to 62° and the pump speed set on its lowest setting.

 

[Samsg30]

In summertime when I’m only using the boiler for hot water, I have my 418 EcoTEC plus boiler set to a max output of 12kw, flow temperature set to 62° and the pump speed set on its lowest setting.

when HW is on, do you see a flashing radiator symbol but the constant on Tap symbol on the screen? This is what I see on my system when it goes in the anti cycling mode. The tap symbol always stays on. If I change the max output to 12kw (if I know how to do it) and the pump mode from 3 to 1, would CH work on some cold days during summer to take the edge out which sometimes needed .. summers are not always hot you see

 

[Johntheo5]

The boiler temp should be ~ 5C > the cylinderstat setting and as the cylinder temp approaches its setoint then you might expect some cycling, is there a gate (balancing) valve with a red handwheel on the return from the cylinder heating coil, if so, shut this fully, then reopen it fully, then shut it full again and reopen it one full turn, should be ~ 3 full turns between fully shut and fully open. Feel the temperature at the inlet coil (top) and the return (bottom), if the return is alot cooler than the inlet then circulating flow too low, if little or no difference then coil possibly fouled with poor heat transfer.

If the boiler is firing for a minute or less then it will help to reduce the max output in the "d" parameters but the higher the pump setting the more the heat extracted from the coil, setting 2 should be quite adequate.

 

[Mottie]

when HW is on, do you see a flashing radiator symbol but the constant on Tap symbol on the screen? This is what I see on my system when it goes in the anti cycling mode. The tap symbol always stays on. If I change the max output to 12kw (if I know how to do it) and the pump mode from 3 to 1, would CH work on some cold days during summer to take the edge out which sometimes needed .. summers are not always hot you see

TBH, I don’t know and I’ve never looked. My boiler is out of the way up in the loft. Yes, 12Kw will be enough for heating in the summer - I only have it on 15/16kw in the winter.

Is your bypass set correctly? With just the hot water, you could be sending a fair proportion of your heated water straight back to the boiler without it going through the heating coil. I actually keep my pump on speed 1 all through the year - 3 bed semi with 10 rads. I’m not a heating engineer but my thinking is that the slower it is going through the cylinder coil, the more chance heat has of transferring to the stored water. Speed three seems very high to me and the water could be passing through the coil with not enough chance to transfer heat.

 

[Johntheo5]

A Ecotec 418 IMO would be doing very well not to cycle with a standard coil based on my tests carried out on a new 150L twin coil cylinder with the oil fired coil heating the upper 100L.
Tests carried out with a stone cold cylinder and 20kw Firebird oil fired boiler with a average flow temp of 70C.
Don't know what the min output of a 418 is but assuming say 4kw then based on my tests it could (with this cylinder) and with the same circ flowrate of 10LPM, start cycling with a cylinder temperature as low as ~ 48C.

 

[Samsg30]

Could this be related to the 3 port valve by any chance? My system is in Y plan and what I noticed is when only HW demand is on, around 1m length of heating pipe becomes hot too but further I touch the heating pipe, it start feeling colder so that shows 3 port valve is pushing water towards the CH side too. The pin on the actuator (silver box on the 3 port valve) moves freely up and down even when hot water demand is off.

So could this be that port is sending false signals?

 

[Swwils]

Could this be related to the 3 port valve by any chance? My system is in Y plan and what I noticed is when only HW demand is on, around 1m length of heating pipe becomes hot too but further I touch the heating pipe, it start feeling colder so that shows 3 port valve is pushing water towards the CH side too. The pin on the actuator (silver box on the 3 port valve) moves freely up and down even when hot water demand is off.

So could this be that port is sending false signals?

Yes

 

[Johntheo5]

If you mean the lever on the diverter valve then as the valve is unpowered with HW demand only there should be resistance on that lever when you start pulling on it, if for any reason its in mid position it should still heat the HW cylinder and the rads as well so even less cycling? except there are TRVs on the rads and all are closed, can you feel the cylinder coil inlet and return?. If you power off the boiler and at its supply then if the manual lever is still floppy then diverter valve needs replacing.

 

[fixitflav]

Hi

I have moved to a different home which has Vaillant Echo tech plus 418 boiler installed with open vented cylinder and a central heating system.
The thermostat on the cylinder is set to 60C and the boiler has two radial dials in front to control the flow temperature, both of which are set to 65C so that it can heat up water to 60C and heat demand should stop.
But boiler is doing short cycling when there's only hot water cylinder needs heating up and no demand for central heating.
I have tried turning the thermostat temperature down from 60C to 55C but making no difference.
Upon going through several posts and documents, I am completely confused as to the correct settings I should have before trying to diagnose the short cycling issue.

Would someone be able to suggest some figures on below questions:
1) What should be the thermostat temperature set at the hot water cylinder at max. (PS: I am OK with 60C to keep legionella bacteria out.
2) What should be the flow temperature settings on the boiler for hot water e.g. +5C to whatever thermostat on cylinder is set to or same as thermostat or lower than the thermostat
3) What is the ideal flow temperature settings on the boiler for central heating
4) Anything obvious I can do to fix the short cycling or is it usual for ecotech plus 418 model to short cycle when water in the cylinder has heated up enough?

In my previous house, I had megaflow and boiler always shutdown as soon as the desired water temperature is reached.

Thanks

Does it cause a problem? The rate of heat transfer into the cylinder is likely to be less than boiler output, so the boiler reaches its control-stat setting, then stops firing, but the pump still runs. After a while (a few minutes) the boiler re-fires and the cycle repeats until the cylinder stat is satisfied.
That's how my system works, cycles about 5 times if I remember right, depending whether the cylinder calls just because of heat loss or a lot of hot water has been drawn off.
But I'm curious why a heat-only boiler has 2 temperature dials. I suppose by dial you mean a rotating knob which adjusts the control-stat setting.

 

[Mottie]

But I'm curious why a heat-only boiler has 2 temperature dials. I suppose by dial you mean a rotating knob which adjusts the control-stat setting.

I think the older 418's had a dial for the temperature of the heating water circuit and another dial for the hot water circuit. Newer ones like like the one I have, have electronic settings where you can have different temperatures for the heating and hot water circuits however, I think that only works when you have the Vaillant controls added to the boiler. If you don’t, the only circuit you can adjust is the heating water.

 

[Johntheo5]

Cycling conditions are a bit of a challenge for Vaillants, especially the higher output ones like combis as their ignition conditions require (or used to??) firing at ~ 65% of max output, they then maintain this firing rate for 60 secs before modulation is allowed which means a relatively long anti cycle time and/or a fairly high target flow temperature, and a sufficiently high flowrate, all (modulating) gas boilers will switch the burner off at SP+5C and then go into anticycle mode. When the 418 fires up then it will output 12kw for 60 secs, assuming a circ flowrate of 12LPM then the boiler dT will be, 12*860/60/12, 14.3C, if the target temp is 65C then the return must be 51C (50.7) to achieve this, you then have a 5C buffer to allow the boiler to modulate, if the return temp is reduced to say 40C by using a suitable anticycle time then the flowtemp will be 54C after firing up giving ample time not to reach 65C before modulation. Cycling will not be a problem under the above conditions.

 

[Mottie]