If the water leaving the boiler is the same or similar temperature as the water going back to it, computer tells the boiler to go to bed and have a nap.
Fan satrts at low speed for ignition sequence and then goes to setting in memory if need arises.
Vaillant EcoTec 428 configuration issues for Hot Water Only
- Thread starter tommcdonna
- Start date
If the water leaving the boiler is the same or similar temperature as the water going back to it, computer tells the boiler to go to bed and have a nap.
Fan satrts at low speed for ignition sequence and then goes to setting in memory if need arises.
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In the interests of establishing whether it's likely to be a limitation of the cylinder causing the problem, I attach a couple of pics to possibly identify the age / type. The pic of the immersion heater head is included with the assumption that it's the same age as the cylinder, it may of course be newer.
Which pump do you have?
Is there an automatic bypass valve?
One mid-position valve or two zone valves?
Is there an automatic bypass valve?
One mid-position valve or two zone valves?
Pump is Grundfoss and is red, I don't know the spec without looking at the info panel on it.
Yes there is a bypass valve.
There is a single mid-pos valve (system is Y-Plan).
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Model name would be helpful; e.g Selectric 15/50, Alpha 15/50 etc.
Automatic or manual (gate) valve?
Does the problem occur only when you have hot water ON by itself?
Selectric 15/50 rings a bell, no idea why it would other than if I'd read the name and numbers before so I think that's what it is.
Bypass valve I'll have to check later. It has a red plastic cap that screws on over the top of the valve adjustment part if that helps.
We've not had the heating on properly yet, but on first appearances it's only a prob when it's hot water only. I'd assumed because it was able to lose heat easier/quicker from the circuit.
Any chance of checking?
Doesn't sound like a gate valve, more like an auto valve.
If the temperature of the water returning to the boiler is the same as that leaving the water, then no heat has been lost. This could be because the water flow rate is too high. Turn the pump speed down - it's probably on 3, so set it to 2 - and see what effect it has; then try 1.
Flow and return temperatures are d.40 and d.41. The difference should be between 10C and 20C.
I wasn't thinking of having the pump at a lower setting all the time, only when the system was on HW only. I was trying to confirm if the resistance of the HW only circuit was so much lower and consequently the flow rate much higher, that this would cause a very small temperature drop across the boiler. A lower should should give a higher temperature drop.
DH, a little surprised at you thought here
It is like having to take the dog for a pee every couple of hours. Sun comes out pump gets set to low speed and a little cloud in the sky one does not know if the pump speed should be set to 2 or three. Come home, house cold, drat pump is on 1, bang it on setting 3...... not very practical.
Idea of a central heating system is to have a plant that will keep you warm without making a big fuss about it.
It is like having to take the dog for a pee every couple of hours. Sun comes out pump gets set to low speed and a little cloud in the sky one does not know if the pump speed should be set to 2 or three. Come home, house cold, drat pump is on 1, bang it on setting 3...... not very practical.
Idea of a central heating system is to have a plant that will keep you warm without making a big fuss about it.
To answer your questions (and other people's)...
Pump is Grundfoss Selectric 15/50, originally set at 3, now set at three as lowering it made no perceivable difference to time taken to reach temp / rad performance / frequency of boiler firing but means the system runs much quieter.
Bypass is honeywell auto valve, have not adjusted this at all, but it's screwed most of the way down.
We haven't had the need to use the heating properly yet, but putting it on for an hour during hot water heating, with only 1 or two rads on, goes a long long way to stopping the cycling (I'd expect a little bit of cycling, that's just life once the system is reaching temperature I would have thought).
Yes, there is a valve on the hot water circuit that can be used to balance.
When boiler cuts out into anti-cycle, flow temp has usually reached 70, return at 60 (both give or take 1 or 2 degrees). After anti-cycle timer has expired and the boiler re-fires, flow and return have usually lowered to 55/53 respectively.
Thats much more the kind of info we need!
That indicates to me that the problem is as expected a combination of too much power from the boiler and too little absorption by the cylinder.
That will be reduced in effect my setting the boiler output to the minimum and by reducing the anti cycle time to a minimum.
Of course setting the boiler to a minimum might not give enough heat you your rads and you may need to have different settings for summer and winter.
In winter timing the HW and CH to the same times will get round most of the problems.
Contrary to what has been stated above, my understanding is that the boiler ignites at close to MAXIMUM power and only turns down to the set value of d0 after about a minute.
Tony
That indicates to me that the problem is as expected a combination of too much power from the boiler and too little absorption by the cylinder.
That will be reduced in effect my setting the boiler output to the minimum and by reducing the anti cycle time to a minimum.
Of course setting the boiler to a minimum might not give enough heat you your rads and you may need to have different settings for summer and winter.
In winter timing the HW and CH to the same times will get round most of the problems.
Contrary to what has been stated above, my understanding is that the boiler ignites at close to MAXIMUM power and only turns down to the set value of d0 after about a minute.
Tony
I agree entirely. I was carrying out an experiment! Temperature differential is inversely proportional to flow rate, so as flow rate decreases the differential should increase. But the OP says in his last post:
So, even with the pump set to 1 the flow rate is too high.
The OP then says that there is a Honeywell ABV screwed most of the way down. That suggests the valve has not been properly adjusted.
There are three Honeywell valve (see Bypass Valves). If the OP can say which he has, I can tell him what setting it should be on.
The boiler ignites at 60 to 70% of its maximum power , the drops back to minimum while it checks the temperature differential, then high gas as set by D0. 
D2 is a difficult parameter to explain, and controls the anti-cycling time. It is calculated on temperature differential. Factory setting is 20. Changing this (as already posted, to 5 or 6) will solve most crappy cylinder installs.
D2 is a difficult parameter to explain, and controls the anti-cycling time. It is calculated on temperature differential. Factory setting is 20. Changing this (as already posted, to 5 or 6) will solve most crappy cylinder installs.
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