Vaillant Boiler not warming enough

[The831Bunny]

The make of your clock and or room thermostat. D.009 figure when the boiler is running for heating.

 

[ripperuk]

The hallway thermostat is Salus RT500RF. Currently I use it on a manual ON/OFF basis as we still have some hot & cold days. Once it gets more colder, I will set it to a daily programme. When switched on, I always have it set to reach 22C.

I'm sorry, but I currently can't get you the D.009 reading as it's pretty hot in the house at night, so I'll try definately for tomorrow. I hope this is okay with you?

Thanks again.

 

[Agile]

OP, the differential measured by the d40/d41 is far too small.

It should ideally be 15-20 C.

When you feel the flow and return pipes into each rad, can you feel a slight difference in temperature on each one?

 

[dilalio]

And get rid of the Salus - they are sh¥te!

 

[picasso]

OP, the differential measured by the d40/d41 is far too small.

It should ideally be 15-20 C.

When you feel the flow and return pipes into each rad, can you feel a slight difference in temperature on each one?

Have no fear captain of the bleeding obvious is here !

 

[ripperuk]

Morning.

I ran the heating as requested, but when I went to menu installer (17) > diagnostics, there is no D.009...ONLY D.008 & D.010.

I also checked the temp for return and out on radiator pipes, but can't tell the difference to be honest

 

[picasso]

Ripper I have a theory that is bugging the life out of me so could you run one simple test for me ? (not trying to step on anybodys toes here) so let the central heating go cold then run a tap for 5 minutes and see if any of the 22mm pipes under the boiler start to heat up.

 

[Agile]

Most people can feel a 5 degree difference in pipe temperatures.

It seems that you may have balanced the rads with too much flow through them hence the low differential.

Although starting with the lockshield only open about 1/4 turn would usually limit the flow adequately. Although you did say that some were fully open.

You might be able to correct the flow rate by just closing each one a little. The amount to close them will depend on how far open you had left them.

The target differential of about 15 C is easy to feel as "hot" and "fairly hot".

The internal by pass is factory set and would not normally be adjusted by an installer. In any case it would interfere with boiler functioning but the differential on the rads would not be too low like yours, in fact would be likely to be too high. So seems unlikely to be any problem in your case.

Setting the maximum power output of the boiler causes it to burn for longer. If set too high it can turn off early and then go through the various preset delays during which time no heat is being delivered to the rads.

Tony

 

[simond]

The internal by pass is factory set and would not normally be adjusted by an installer. In any case it would interfere with boiler functioning but the differential on the rads would not be too low like yours, in fact would be likely to be too high. So seems unlikely to be any problem in your case.

The internal bypass is of course set in the factory, but installers are encouraged to adjust it where necessary.

When an installer fits an ecoTEC MKII, and it doesn't warm up properly, they often try adjusting the bypass in an effort to cure it. Therefore it is not at all uncommon to find an ecoTEC Mk2 with the heating Kw set too high and the bypass adjusted.

Like most things, you learn a lot about boilers and how they go wrong simply by either fitting and or repairing a lot of them. Some on here claim huge experience but that is at odds with the frequency of posts they make on this forum and elsewhere.

 

[hertsboilers]

OP, you have been lucky so far, as many experienced boiler men on here tried to help you, particularly by @Steelmasons, @The831Bunny, and @picasso. It might be a simple fix, but it is always better by our own diagnosis on site. So it might be the time to call Vaillant their own engineer in.

 

[ripperuk]

Ripper I have a theory that is bugging the life out of me so could you run one simple test for me ? (not trying to step on anybodys toes here) so let the central heating go cold then run a tap for 5 minutes and see if any of the 22mm pipes under the boiler start to heat up.

I did this test and ran the tap for 5 mins with CH turned off. The 22mm copper pipe on the bottom left of the boiler is definately heating up

@Agile - I will totally close all and just open them a 1/4 turn.

@simond - Right, so it's really a complex thing to change or adjust.

@hertsboilers - I know mate and I'm ever so grateful for everyone's advice. Just really frustrated that so far we haven't been able to tackle this problem. I will wait for a few more answers and then I'll contact Vaillant.

Thanks again.

 

[picasso]

I reckon your diverter valve is passing, so you got the flow running straight across the plate heat exchanger into the return, that's why its modulating down .

 

[ripperuk]

I reckon your diverter valve is passing, so you got the flow running straight across the plate heat exchanger into the return, that's why its modulating down .

So what does this mean and how can it be tested or fixed?

 

[The831Bunny]

Indeed if the DV is passing the return temperature will be higher than normal. To confirm, look at D.004 (preheat temperature of the plate exchanger). Normally it will show a static temperature when heating is operating of around 45-50C if the pre-heat (Comfort/Warmstart)is enabled. If the DV is passing D.004 will fluctuate, eventually rising and rising as the primary water heats the plate.

A high return temperature can also be indicative of a high resistance system. The internal bypass is set to 250mb, rather low in most cases as @simond as mentioned. It will certainly be bypassing though if the radiator valves are only opened a ¼. Sorry @Agile by that is tosh advice. The radiator with the most resistance on the circuit (usually the one practically the furthest from the boiler, but not always) needs to be fully open on the lockshield valve, and other radiators progressively reduced working back to the boiler. Rule of thumb too is larger radiators need more throughput than a postage stamp rad sized one. The key is they should all heat evenly and at the same time. A process that in a domestic situation a professional will draw on much experience.

My bad re D.009. You have the later ecoTEC which shows the 'requested' heating flow temperature at D.005. If you had Vaillant controls, these would request a flow temperature which could easily be lower than the maximum set on the boiler display. As you have a Salus thermostat this doesn't apply. You COULD be losing RF contact though before the boiler reaches temperature, but thats another angle...

 

[ripperuk]

Thank you. Being a novice, I don't understand much of what you said (SORRY!). Is it possible you can tell me exactly what I need to do?