Concerns on Vaillant ecoTec plus 428 system boiler

[madjeff]

Would much appreciate some answers to observations I have made regarding my recently installed new boiler. I have an open vented system for heating and a non vented mains pressurised hot water system.

The system is wired in traditional S plan mode, using the supplied boiler contacts 3/4 to control the boiler. The only deviation is the pump which is now fed from the terminals supplied within the boiler.

Query 1. As the pump is now controlled from the boiler and not the zone valves via the stats, the pump stops after set tempuature is reached and the pump overrun timer times out. Result hot water stat set point 52 deg. is rarely reached as control is effectivily set with the boiler temperature.?

Query 2 When boiler temp is reached the boiler goes to overun mode approx 5 mins. During this period the pump continues to run even if all zones valves are closed due to stats reaching set points?

Query3 I have a honeywell ABV type DU144 fitted. When the boiler is running the bypass valve gets very hot indicating that a substantial flow is being diverted. This happens even when all rads are fully open and HW is fully open. The Honeywell leaflet suggests this valve should remain closed and only modulate as flows are restricted e.g when TRVs begin to close. I removed trhe ABV and run water through it measuring about 2lts per min.? Does this mean its faulty or just not designed as a tight shut off.?

Query4 Valiant quote about 1250 Ltrs/Hr. as a minimum flow. Is this correct, as it represents around 50% of the my total pump capacity, adjustable range (0-2500 ltrs/hr maximum 4/6 Bar head)

This is the first time I've upgraded my boiler in over 20Years, so I'm hoping that the latest operational designs have moved on and no longer work as I expected them too, but currently it all appears a bit odd to me.

Gratefull for any enlightenment.

 

[gas4you]

Firstly, good luck with a 400 series.

The hot water control on the front of the boiler will have absolutely no effect on anything unless you have a VR65 unit fitted and a Unistor cylinder with the VR10 ntc fitted.

You need to set the main boiler stat (bottom one) to a minimum of 65C to enable the HW cylinder to get to 60C.

Pump over run sounds as if it is correct at 5 mins. This is the factorey set time. I always have set mine to 7 or 8 mins with d1.

The honeywell abv sounds as if it has not been set right. It should only open if the pump is running and all trv's are shut and HW circuit is off. Generally I have found the setting of approx 3.5 covers most installations.

Your pump should always be set on maximum speed with these boilers (3)

The HE does not like low flow and heat

 

[madjeff]

"Firstly, good luck with a 400 series". don't understand, perhaps you could expand on this statement.

your comment on abv, as I said valve passed 2 litres /min pouring water directly into it. = Zero diff pressure should equal no flow. My question was is the bypass line being always hot, and a minimum leak rate of 2 litres per min normal.?

My other main point was the running of the pump during overrun without being called for by the hot water or heating circuits. The other point was that the pump stops running after pump overrun even though a demand still exists from heating or water. I could control the pump directly from the water/heating zone valves, but that would override any commands that vaillant have built into the boiler e.g pump overrun.

Thanks for your comment regarding highest speed, duly noted.

 

[AlanE]

The ABV should remain closed during normal operation ie when there is a demand for DHW or CH.

When these demands cease the pump continues to run to dissipate excess heat in the boiler. As the motorised valves have now closed the water pressure opens the bypass and all the flow is via this route.

 

[madjeff]

The ABV should remain closed during normal operation ie when there is a demand for DHW or CH.

When these demands cease the pump continues to run to dissipate excess heat in the boiler. As the motorised valves have now closed the water pressure opens the bypass and all the flow is via this route.

Thanks for input, clearly the ABV is faulty. Your second point confirms is is normal for the pump to operate against closed valves, as the ABV will ensure minimum flow is maintained.

My last unresolved query is why does the the pump shutdown following the 5min pump overun timer period when the the system is still calling for it to run? The boiler does restart after a few mins but it creates a lot of cycling and during that period there is no flow to the rads or cylinder.

 

[David937]

My last unresolved query is why does the the pump shutdown following the 5min pump overun timer period when the the system is still calling for it to run? The boiler does restart after a few mins but it creates a lot of cycling and during that period there is no flow to the rads or cylinder.

Does a flashing radiator symbol flash on the display after the pump goes off?

 

[madjeff]

Does a flashing radiator symbol flash on the display after the pump goes off?[/quote]

Yes it does, and I cant find out the signifcance of the flashing symbol, can you enlighten me

 

[Biggles..]

temperature reached,or waiting for heat input demand.

Much easier to press the i button during operation as the S codes tell you what your boiler thinks its actually doing

 

[gas4you]

I would clarify that slightly as boiler stat temp satisified, but a call for heat from external controls is still present.

 

[Deleted member 105431]

have you done a heat loss calc for the house and range rated accordingly? this is very important on the 400. do you have the unistor and vr65?

The pump MUST be wired directly into boiler and be on maximum (3) for correct performance.

 

[mickyg]

If you turn the controls off does the display remain on the front of the boiler?

 

[madjeff]

have you done a heat loss calc for the house and range rated accordingly? this is very important on the 400. do you have the unistor and vr65?

The pump MUST be wired directly into boiler and be on maximum (3) for correct performance.

2nd question first. Yes, I wired the the pump directly to boiler and wired the zone valve dry contacts to the so called room stat terminals 3/4 removing the link.

I carried out a heat loss calc prior to purchase/specifying boiler size. I'm happy with that aspect. I did not purchase a vr65 instead using a conventional S plan. I have a new cylinder the 300 ltr. Heatrae solar megaflow (pressurised) no solar fitted yet.

Since my last post I have found a different valliant manual online with much more information than the one supplied "Vu 656/4 installation and maintenance for the heating engineer". I think your comment on range rating is significant. currentely I'm only using hot water and the boiler output is set to maximum 30KW. I have set this down to 10KW and is currently working perfectly, I hardly notice the boiler is running it is so quiet. I will monitor this and re-range accordingly as the outside temperature falls and heating demand rises. Prior to resetting I had the much discussed (on this site) dreaded S53 following a cold start this morning. I assume S codes don't need resetting and resume when back within operating parameters.

My only other outstanding problem was the pump. I am now satisfied that it is ok for pump to run against closed zone valves as the ABV assures minimum flow maintained. I have now discovered D18 pump mode which allows me to set either return, non-stop or winter. currently set to factory default 0 (return) The complete logic of these modes was not explained in my manual but the heating engineers manal describes them in slightly more detail. 0 = Overun which for no particular reason I have increased to 10 mins. non stop is discribed as run-on which appears to, in addition to overun hand pump control over to the external stats. which was what I was looking for. The third called winter is also called intermittenent, and I still dont quite understand the purpose of this mode.

The pump options has now created a choice dilemma, perhaps overun mode with just water heating on is more efficient, as perhaps after the boiler stops, continued running of the pump will cause the HW to lose energy whilst circulating back around the system. Any views on this thought.?

Finally a big thank you to all who responded, heres hoping publically displaying my learning curve on my new boiler will help others in a similar situation in the future.

 

[simond]

Perhaps you should fit weather comp to your 4 series.

It will give you far more knobs to twiddle and if, as I am sure you would ensure, it is set properly, you will find the boiler and associated controls work in best harmony and efficiency.

The HW thermo sensor can be inserted into the Megaflo but you will have to alter the wiring to ensure the Baxi OH stat closes the two port valve. Alternatively just use the wired unintelligent cyl stat option.

In both cases you'll need the VR65 wiring centre, a VRC430 controller, and thats about it. Less than £200 all up.

NB: The 630 is a better boiler with a two speed pump but not suited for open vented primaries.