Vaillant ecoTEC + 831 - operating correctly?

Hi all, perhaps you can educate me as to how my heating system is actually performing compared to my perception? Apologies for the long winded following but I think it is important to include all info.


The boiler is a Vaillant ecoTEC+ 831 with Honeywell wireless programmer (CM927).


I have the programmer programmed with all 7 days the same and using all 6 time-zones. My query is as follows: One of my time-zones is 0930-1500 target temp set at 18 degrees on the basis of us normally being out. If we are at home I over-ride the 18 with 20. The temp usually gets to 19 (according to the ‘room temp’ on the Honeywell) and no more


29 Jan 2019 - I did a mini monitor/test – log as follows:

10.00 Over-rode the 18 with 20

10.40 Stat – no demand. Target 20, actual 19.

10.45 Stat demands (green light on receiver). Boiler fires, burner indictor rises to above 1/2 way. Flow temp rises from 43 to 52 within 5/6 seconds but then the burner drops to below ¼ position. Flow temp drops to 42 and stays there until…

10.53 ..when the demand led extinguishes. Stats says – target 20 actual 19.


10.55 Stat demands. (target 20 actual 19) and as above:

Burner rises to above ½ way for about 5/6 seconds then drops to below ¼ and flow temp goes from 43 to 50 and back to 47 during this short period until:

11.00 ….when the burner rises to ½ position, flow temp up to 57 degrees (return temp only warm)

11.03 Demand led extinguishes. At Stat – target 20 actual 19….still.

At 11.35 Stat temp of actual 19.5. A full 95 mins after overriding the 18 with 20.

My boiler is still under warranty via my local company who installed it. Had a leak recently, and my company called out Vailliant (suspected diverter leak). Vailliant came out, replaced the diverter (removed plastic diverter and replaced with brass one). Otherwise the heating has worked ok but I have been disappointed by the slow response to requested change as per my query here. I have raised this several times with my maintainer but despite changes to some parameters, does not seem to have made any difference. Parameters changed - Target Flow Temp = 75 degs, Boiler load set to 19.5 KW ( I have calculated my total radiator output to be in the region of 14KWs simply by adding up the rad values.


Consolation? Hot water fantastic !

If this is normal operating procedure then I will have to live with it but would like a view from you pros.


I have ordered a pipe thermometer to check out temp drop across system and individual rads, so may have more info to add soon.


Thanks for having the patience to read all this !!


SjH

You may have a badly balanced system. Try checking the flow and return temperatures at D.40 and 41 with the boiler running the heating after 10mins. You’re looking for 15-20C difference. You may improve things by adjusting D.14 to 5 and balancing the radiators.

There are four or more ways to control the boilers output and room temperatures, the basic idea is either the TRV controls room temperature or a modulating thermostat with a modulating gas boiler, however oil boilers don't modulate to same extent so there are off/on thermostats with algorithms included which are designed to stop the temperature over shooting. (Anti hysteresis) The simple method is before it reaches set temperature it starts to cycle off/on changing the mark/space (on/off) ratio as it gets closer to target.

I am also unsure as to best options, as every time a boiler switches off, any heat in the boiler is lost up the flue, and also the boiler has some thermal stress, so theory says turn up/down not on/off. However using a modulating thermostat in the main they monitor one room, and really we want every room independently controlled.

So we get thermostats like Nest 3 which will modulate boiler and connect to the TRV electronic heads, but it means all heads connected are at same temperature, I am told EvoHome although it allows independent control as standard is mark/space control and you need an extra bit to work with OpenTherm as a modulating controller.

As one starts to look at the options the price seems to go up, so starting at the top and working down, in order to heat quickly as and when required the amount of water and the amount of metal in the radiators needs to be kept to a minimum, you don't want to waste time heating the water first, so a car type fan assisted radiator is likely the best, output is controlled by altering fan speed, and because it is forced to circulate the whole room is at same temperature. See the Myson iVector as an example.

However they are expensive, and it is debatable if we want whole room at same heat, blowing air across windows will increase the heat lost, allowing the area in front of windows to be cooler may be a better option, and if the sun hits the window instead of areas at 32°C where sun is hitting and main room at 20°C you will even it out so whole room at 24°C. Yes the fan assisted is fast acting so when the sun hits the window it switches off quicker, and it takes up less space. But the building management system required to relay it's requirements to boiler is also expensive, so other than in kitchen where kick space heaters are very good, the fan assisted is not really an option for the normal home.

So I tried a wireless thermostat and standard TRV first, idea was the TRV stops over heating, and the wireless thermostat is placed in the room occupied, so I could move it around, it was cheap and had no fail safe, but before it was fixed to oven in kitchen (another story) I tried it in many positions, what I found was at 90° to radiator it had a very large hysteresis, on the opposite wall it got the room too hot as it was an outside wall so cooler than room, on a tea trolley 2 foot from radiator set a little high to compensate for being so close it worked A1. The wireless connection got weaker and weaker and it was taken out of service, then used just to get a morning boost.

However it became plain that measuring the temperature close to the radiator actually worked, so then looked at the TRV and wondered if they were the best option, so 4 of the old wax heads have been swapped for electronic heads to control room temperature, however in this house there is a slight problem, the TRV's are fitted to the return side of the radiator, although the TRV is bi-directional, if fitted on supply side the valve head senses the heat quicker so that reduces the hysteresis. To counter fitted to wrong side of radiator I have used the lock shield valve, by careful adjustment I now have four rooms at exactly temperature set, within on degree C.

However it raises the question would it have worked just as well with the wax heads had I adjusted the lock shield valves? Problem with wax head is no scale to set temperature to, just *, 1, 2, 3, 4, 5, 6 so how do you know if the TRV or the lock shield valve needs adjusting?

And to alter temperature through the day, only option is an electronic head, the terrier i30 seems to be the cheapest, at around £18 far cheaper than the £40 I paid each for mine.

So let us assume half the rooms with wax and half with terrier i30 heads, the half with wax kept around 17 - 18°C the ones with electronic heads temperature varies through the day, boiler modulates with the temperature of return water, so an efficient system with very little or no hysteresis seems perfect, and in heart of winter likely is, however as summer approaches it has a problem.

Gas boilers typically give 6 to 28 kW output, as with a car the lower the output the more efficient, or at least it should be, but once it hits that lower limit it starts to cycle off/on, although any cycle software can reduce the cycling, it will not stop it, so unless you manually turn it off, it will continue to fire up all summer.

So we want something to switch it off completely when not required, the thermostat used to do this should not have any anti hysteresis software, in fact the old mechanical thermostat without the neutral connected is likely the best option, it needs to be in a room kept cool, as we doing want heating firing up on a summer morning when latter we are going to get too hot, also a room with no alternative heating, and no door to outside. The thermostats sole job is to turn off the heating on warm days, it does not control room temperature, in most houses there is no such room, however the hall often ticks all but one box, as it has door to outside, but in general it is good enough. Fitting a TRV in the same room needs the wall thermostat and TRV to be set to complement each other, so TRV set to 17°C and wall thermostat to 18°C the hall radiator will reheat room when door to outside opened quickly, but will stop before it switches off the wall thermostat, this does work, it's what I have.

However the design of house makes a difference, with an open plan house with an OpenTherm enabled boiler then a modulating wall thermostat in main room likely a better option.

Nest can link to Energenie MiHome TRV heads so with Nest in the hall and hall TRV linked it could modulate the boiler A1.

Each home is different, it is all well and good the government saying homes should be zoned and living and dormitory areas should be independently controlled, this works well with an oil boiler which is off/on but does not really line up with a gas modulating boiler.

Also this house takes ages to cool, if the system over heats a room, then it takes ages to cool again, switching heating off over night likely temperature will not drop more than 4°C, however last house no heat over night and it got really cold. Heat raises so bedrooms upstairs unlikely to get too cold, but a bedroom on ground floor can get very cold.

And if the thermostat is 1 or 2°C out then set it 1 or 2°C high or low to compensate, the anti hysteresis software in my TRV heads is too good, so 7 am set to 24°C then at 8 am down to 20°C once at 20°C it will hold there, if I did not cheat it would be 11 am before actually at 20°C.

The boiler once it gets a demand from the stat will fire at about 60-70% its maximum rate (simply thats the optimal rate to light the burner)

Once the burner is lit, the boiler will run in its lowest output for about 5 minutes to circulate water round the system before it then ramps up to the set heat output (the 5 min delay on low rate is not adjustable and is common on lots of new condensing boilers)

Out side of this the boiler has done its job and can only come on and off by a signal from the room stat, the distribution of heat in the house and how/when the stat calls for heat is dependant on the stat/system.

It should not happen, but it does, installers don't set the lock shield valves, they are left wide open, as a result hot water returns too early, so boiler modulates ahead of when it should, so possibly only running at maybe 10 kW instead of 28 kW as each room warms up the TRV closes and water is then forced to next room, once the whole house is warm the TRV's ensure the water is shared between radiators, it is only warm up form cold that is affected by not closing the lock shield valves to required amount.

But normal complaint is cold radiators, which does not seem to be your complaint.

Thanks all for those informative replies. I fully agree with the balancing of the system sometimes not being done at install so have started there - I am sure the boiler is not faulty, just needs a little understanding..ScottishGasman has described the operation to a tee so agreed, the boiler appears to be doing it's job. And thanks to ericmark, I appreciate the 'algorythmic' theory of operation - I had to explain it to the guy who did the first years service!! Made me think of 'old dogs and new tricks'!

A couple of very relevant points made there. My nearest radiator to the boiler is a bathroom, (The property is a bungalow but the loft has been converted so can be treated like a house with a large floor area) and I found the lockshield valve fully open on the bathroom towel rail, so I temporarily closed the lockshield completely (as a test), making a big positive difference to the rest of the house. I have put it back on with reduced flow at lockshield and am awaiting a pipe thermometer to test temp drops across system and all rads to allow me to properly balance.

I will respond with results when I get the thermometer - but a last comment, the pipe thermometer was only a fiver on ebay but maybe good enough to give an indication of how far the balance is out?

Regards to all

S

Start balancing with the radiator physically the furthest away from the boiler fully open on the lock shield valve, the one closest to the boiler closed, then a ½-¾ of a turn open, and the rest proportionally in between. Towel rails are notorious for robbing pump head. Also close any external bypass fitted on the system, you don’t need it. Vaillant supply a nice adjustable automatic one in the boiler set at the mid point to suit most installations.

I would still change D.14 to 5 to see the difference, you can always reset it to auto at your leisure.

You could also change the cycle rate on the 927 to 3 cycles per hour from the standard 6 to see if that helps. Check the 927 installation instructions for how to do that.

As to the ‘detailed’ post up the thread.... a little knowledge is truly dangerous!

Thanks 831Bunny, I did mean to include comments re D.14 earlier.

1. Agree first para - have no external bypass and have read up on Vaillant's auto one.
2. Interesting re towel rails - not heard of that before, but fits with my findings.
3. In my Installers manual it suggests that D.14 is not adjustable (although there is reference to D.19 'two stage pump')
4. Will check out the 3-6 cph for 927.
5. I have no probs with 'detailed' posts - I am a bit of a tecky in my old age and it keeps the ''grey muddle between my ears' on it's toes!

Thanks again all.

S

If your boiler is post 2012, and has no knobs for temperature adjustment, D.14 is adjustable, and is the code to adjust the five speed pump. D.19 is two speed pre 2012. Auto pump operation is fine on a 100% balanced and piped system. If there are more than three rads off of a 15mm run, or two off of a very long run of 15mm, then as soon as the return warms from a closer rad, the boiler will try and widen the delta T (and the efficiency) by reducing the pump speed. The result is that rads offering a high resistance lose the flow rate required.

Thanks Bun. My boiler was installed in Sept 2013 so assume your post 2012 will apply. I have not checked D.14 yet because since I did a bit of 'layman's balancing' I am getting far better results. The nearest rad (bathroom towel rail) lockshield was wide open, so I have that now well reduced, and also a similar situation with another 'near boiler' rad. Feels a lot more cosy cosy.

When my budget thermometer arrives I will do a full check on temp drops and post findings.

So far, thanks to all for reading and contributing.

S

Hi all, a final note.

Said thermometer arrived and was swiftly consigned to the bottom drawer. Useless. I then decided to buy an infrared one, not much dearer but could be used for loads of other things. Anyway it arrived and is very impressive in appearing to be accurate and instant readings. I did a check across all radiators and found variable but not outrageous temp drops, reasonably consistent, so was quite happy that the bit of 'amateur balancing' I had done earlier had worked out. I had found two rads close to the boiler that had lockshields fully open, so shut them down a bit - made a big difference to the rest of the system especially the room with the programmer in it - temps requested were being reached comfortably whereas before I found them always dropping short.

Having the new toy, I have been using it to check everything, from the temp of my tropical fish tank to the temp of the cat! I also (probably totally irrelevantly) pointed it at the top middle of all rads last night whilst heating was on and got roughly 50 degs on all. (+/- 2).

Probably the only issue I have, and it may not matter now, is that I am struggling check the drop across flow and return at the boiler. I am not too sure when to actually test that and get big temp swings as the boiler performs it's management (or trickery...)

So, I am happy I have a correctly operating system and thank you all for being so patient and helpful.

S

The only reliable way to test flow and return temperatures at the boiler is to check the readings at D.40 (flow) and D.41 (return) after the boiler has finished start up on low burner, but before it modulates on the set flow temperature.

So run the heating from cold, wait for 5mins for the burner to increase to the heating gas rate, then check temperatures.

Ideally you should get 15C-20C difference between flow and return. Now the system is properly balanced reduce D.0 if over 20C difference, or increase if under 15C. Jobs a good’un!

Apologies - better late than never. I got no indication there had been another reply after my last post so didn't see Bunny's - thanks for the reply Bunny.

A good further way down the line and with things working as expected I have pursued no further changes. Incidentally, I had a 'firing up' fault a recently whereby the lady telephonist at my maintainer insisted 'it was definitely the room thermostat'. I re-assessed her remote diagnostics expertise after they changed the PCB !!

Bi to all and thanks again.

If your new toy doesn't have an emissivity setting then bin it...it will give unreliable readings.
Your hands are sufficient to balance the rads, pull up the D40/41 temps if necessary.
If necessary slow the warm up by setting the boiler kW output lower and temp turned down...adjusting up as you improve the balancing.
Installers don't bother balancing systems due to the fact that most radiator lockshields are utter carp and will leak as soon as touched...and customers won't pay for an upgrade.
What they think they'll save in parts/labour they lose on the gas bill through excessive boiler cycling.

Thanks Gasguru. I think I have sorted my issues now.

My last post was really to acknowledge that I had had a response from Bunny (some time ago...) but had not responded with thanks (due to being unaware of his response.)

Any further readers please understand that I consider this thread closed now and Thanks to all.

Steve