Controls for a ecotec plus 428 boiler

[jeffridj]

I had an ecotec plus 428 boiler fitted in early 2011 and at the time kept my AQ6000 weather compensating controls. The AQ6000 unit is in the living room.The problem I now have is that when the whole house is up to temperature the heating goes off as it should but doesn't come back on until the temperature in the living room is about 3 degrees or more below the set temperature. This means it starts to feel decidedly chilly before the heating comes back on. Does it sound like the AQ6000 is faulty?
If I was to replace the AQ6000 I was thinking of going over to use Vaillant controls. I don't think I want a weather compensator any more, so I thought of the VRT350 but I'm told that this needs the VR66 wiring centre which is not available yet. Is there any alternative to the VR66? If not, what controls would you suggest?

Thanks for reading,
Dave.

 

[Agile]

As far as I can see your AQ6000 is ONLY a programmable thermostat and NOT a weather compensated control.

There would usually be a setting for the hysteris, often 0.5 C or 1.0 C, but I dont see where that is on yours.

It could be performing badly because its in a room with radiators too close or badly set.

It should be capable of working adequately with that boiler. Vaillant controls are pretty expensive and I suspect you may pay a lot and get little advantage.

Certainly weather compensation is very good as long as you are not a fiddler. If chosen they need to be left alone to do their job and NOT touched once set up.

Is your house really so big that it needs a 28 kW boiler? Did you or the installer do a whole house heat loss calculation before choosing that?

As a guide a typical 30s semi needs about 10-12 kW !!!

Tony

 

[DP]

Tony wrote

As far as I can see your AQ6000 is ONLY a programmable thermostat and NOT a weather compensated control.

What with an external sensor and pipe sensor fitted as part of the system to eek maximum heat from the boiler, it is more than 'ONLY a programmable '

 

[jeffridj]

As DP says it is indeed a weather compensator and the system is sized for the house. It's a 4 bed detached. This has only started happening since the attic had extra cladding fitted, which may be a coincidence or maybe the house was not getting up to temp before in the cold weather!
When the problem happens the set temperature on the thermostat is showing as 23 and the actual temperature is showing as 20 before the controller finally asks the boiler for some heat.

I was thinking that the Vaillant controls may save some money in the long run as they claim to run the boiler for longer in the condensing mode?

 

[Agile]

I was reading the setting up instructions and there is no mention of setting curves or anything normally associated with weather compensation.

Furthermore it only seems to do on/off switching on the boiler. That being the case its not clear what advantage external sensing will have on comfort or efficiency?

The normal expectation is that a W/C controller will adjust the boiler flow temperature so that it remains in condensing mode more of the time.

Tony

 

[Aragorn84]

I had a honeywell controller in an old house that attempted to do some sort of rubbish compensation, might have even been the same model. It was a piece of crap.

You'd set temperature time blocks during the day, ie 20c between 8am and 9am, 15c between 9am and 5pm etc and it would fire the boiler up early based on the ambient temperature, in an attempt to meet the target temp at the time you set on the panel.

Was pretty hopeless though as it used to fire the boiler at about 4am in winter because it figured thats how long it would take to get the hallway where it was located up to 20c by 8am...

 

[jeffridj]

Agile - You got me thinking about how it's supposed to work.

I believe it learns how long it takes to get up to temperature given the difference between the outside, inside and requested temps and puts the heating when it believes it will be able to get up to temperature by the requested time. It's supposed to do the same in reverse as well.

It also does something with the flow and return temperature sensors and that could be the problem. It was rewired when the new boiler was fitted, as the boiler now controls the pump. Originally I think (but not certain) that when it was up to temperature it was supposed to put the pump on without the boiler about every ten minutes and if there was little difference in flow and return temps it would not put the boiler on untill the temp dropped significantly.

If anyone has a wiring diagram of what it should be now it would be great, mine was lost many moons ago.

 

[Agile]

All that those early controllers ever did was to vary the heat up times.

That was an advantage with the old non-modulating boilers but has little benefit with modern boilers.

The generic description was optimum start.

More relevant to large office buildings with a longer warm up time than a house. And off all weekend too.

Tony

 

[jeffridj]

OK thanks, back to the original question then.
I'll change the controls to Vaillant.

I thought of using the VRT350 but I'm told that this needs the VR66 wiring centre which is not available yet. Is there any alternative to the VR66? If not, what controls would you suggest?

 

[picasso]

have a look at the vr65 it should what you want with a different vaillant stat/programmer

 

[scoobydo123]

Be careful with what you choose as you could be in for a whole world of pain. Can you do a test for me, call for CH when up to a flow of say 65c turn the boiler down to say 50 the boiler will then switch off. Now crank up the boiler stat again to 70c and see if the boiler only fires for around 15 seconds only? You can also do a similar thing with the DHW stat ie when satisfied turn the tank stat up a bit and wait for the flow and return to get near to target temp. Then turn stat down so the boiler goes off, then up it again and see if you get another short cycle. If your boiler cannot get past the 50 seconds intial burn after the first extended burn you may well find going for advised controls may give you a headache.

 

[Agile]

I did ask him about the heat loss of the house and why a 28 kW boiler has been chosen.

He did not answer!

As you suspect, if he has an oversized boiler he may well have problems!

 

[jeffridj]

Agile - I did answer - I said it's a 4 bed detached house and it has been sized correctly. The plumber who fitted the replacement boiler confirmed that it was the correct size.

Scooby - I will try the test you mention and let you know what happens.

 

[Agile]

How do YOU know its sized correctly? Just the say so of a nupty plumber?

Unless you have no loft insulation and single glazed windows and solid walls then I just dont believe that!

You could prove its undersized by seeing what d0 in the boiler settings is currently at. Then reducing it to do = 16 kW which is far more likely.

I suspect your plumber was a nupty. Do you think he even made any calculations? Do you know how much power he allowed for heating the hot water cylinder?

D Hailsham may offer to calculate it correctly for you if you are lucky.

Tony

 

[jeffridj]

As I'm not a plumber is all I know is that the plumber who fitted the original boiler was a well respected plumber in the area and he sized the original boiler. The plumber who fitted the replacement was recommended to me and he agreed that the size was correct. I have no idea what D0 is or how to read it, but if you can tell me I will happily report back.