Vaillant boiler always exceeds set temperature

[kilodelta]

Hello. I have a Vaillant EcoFit boiler that is a few years old. We had our annual service last month and ever since then I’ve noticed something unusual.

The radiator mode temperature is set to 65C but it always exceeds that, hits 70C, and then stops and the the egg timer comes on. If I check the boiler status, I see either S.07 (pump overrun) or S.08 (anti cycling mode).

Is this normal? I called the engineer and he said it was. I’ve noticed the egg timer would sometimes come on if the Nest turned the heating on and off in quick succession, but not every time it fires up.

Thanks.

 

[Scott_D]

It’s trying to stop itself cycling on/off too often. The same as doing lots of short journeys in a car isn’t good for it.

 

[John.g]

Its only normal if the boiler minimum output is greater than the heating demand, most/all boilers operate in this fashion, ie they will cycle if the boiler temp is > SP+5C. It is not normal if the heating demand is > than the boiler minimum output. Some Vaillant's even with the heating demand > the boiler output were cycling at SP+3C.
So is your boiler cycling when the heating demand is > the boiler minimum output?.

 

[kilodelta]

Thanks for the replies. This is going to sound dumb but how can I quantify the heating demand? We have a system boiler that goes to both an unvented cylinder and the radiators.

 

[John.g]

How many rads are "on" when this is happening, how many installed rads in total?. Is this only happening since the last service.

 

[Scott_D]

I your cylinder thermostat is set to 60 and your boiler set to 65 this might not be helping

 

[John.g]

Should also have said that if the boiler is doing this from a cold start say in the morning then definitely something wrong, the boiler should fire at 100% until it approaches its SP (65C in your case) and then modulate down to maintain its SP, there will be some degree of overshoot, 3C would be typical before falling to a steady 65C, next time it fires up, watch the boiler temperature very closely to see what level it reaches.

 

[kilodelta]

I’ve only noticed this happening since the last service. I think the engineer didn’t screw on the top case all the way and it makes a rattling noise when working hard. This is why I looked.

We have the same number of radiators- 7.

The hot water is only on for an hour and a half in the mornings and evenings and the overshoot happens when it’s off. It’s set to 65C.

Is there anything I can try myself?

 

[John.g]

"The radiator mode temperature is set to 65C but it always exceeds that, hits 70C, and then stops and the the egg timer comes on. If I check the boiler status, I see either S.07 (pump overrun) or S.08 (anti cycling mode)."
Are you saying that the boiler cycles on/off always and never runs for any length of time continuously?
You also say, above, it always exceeds this, you have 7 rads, do they have TRVs (thermostatic radiator valves) or/and are they zoned?
If this is happening always with 7 rads on then clearly a problem, just switch the boiler off and on again and watch status d.40 (heating flow temperature) very carefully once the boiler fires up and see does it then reach exactly 70C and burner cut out. It should reach ~ 63C and then modulate down, the temperature should then fall to, and maintain 65C. except that all the TRVs, if fitted have closed in, or there is only one zone open with only a few rads on it.
Also when/if it is running continuously can you also check status d.41, heating return temperature.?

You also say above " The hot water is only on for an hour and a half in the mornings and evenings and the overshoot happens when it’s off. It’s set to 65C." Is it also or only overshooting on hot water only?.

 

[kilodelta]

How do I check status D.40 and D.41? I haven’t checked if it happens only when the water is enabled. The cylinder and the radiators use the same temperature setting (we only use the dedicated radiator input/output pipes, the water ones aren’t connected).

It seems like it rarely runs, which is why I came to the forum. I’ve observed it slowly rising to 70C and then immediately cutting off. I need to monitor it more.

Most of the radiators have valves. There are no zones.

We’ve always had low gas pressure when the boiler is running on max. Cadent always have to come out and check. They usually leave it but this time (after the annual inspection) they moved our meter outside and replaced the pipe. Could that have anything to do with it?

 

[John.g]

If you are not familiar with calling up the codes then I wouldn't try now.

If the boiler is climbing to 70C especially say in the morning after a cold start when all the rads will/should be calling for full heat then definitely a problem as the boiler should as stated above settle down at 65C and continue to run.
Get the service person back as he has to replace the boiler casing properly from a safety point of view even if the boiler was running properly.

 

[Amz84uk]

kilodelta, did you manage to resolve this issue?

We have a Vaillant system boiler, and had it serviced last month. With the heating now required in the mornings, we've realised that the radiators don't warm up fast enough.

Our boiler temperature is set at 70 degrees, and last year, as soon as heating (or hot water) was required, it would fire the boiler to 70 degrees instantly, to warm up the entire house rapidly. Since the service, it's heating up slowly.

I have checked the boiler temperature and it goes from 20 degrees (when off) to around 40 degrees for 10-15minutes, then takes a break (radiator symbol flashing) for around 10 minutes. It then fires up again and takes the temperature to 65-70 degrees, but it takes at least 30 minutes, whereas previously it used to be instant.

What could be the issue here?

 

[kilodelta]

kilodelta, did you manage to resolve this issue?

We have a Vaillant system boiler, and had it serviced last month. With the heating now required in the mornings, we've realised that the radiators don't warm up fast enough.

Our boiler temperature is set at 70 degrees, and last year, as soon as heating (or hot water) was required, it would fire the boiler to 70 degrees instantly, to warm up the entire house rapidly. Since the service, it's heating up slowly.

I have checked the boiler temperature and it goes from 20 degrees (when off) to around 40 degrees for 10-15minutes, then takes a break (radiator symbol flashing) for around 10 minutes. It then fires up again and takes the temperature to 65-70 degrees, but it takes at least 30 minutes, whereas previously it used to be instant.

What could be the issue here?

No, I never resolved the issue. I've put it on hold during the summer months and I'll revisit it when it starts getting colder. Your issue sounds identical, however. Please reply here if you have someone look at your boiler sooner.

 

[Deleted member 120897]

@Amz84uk - who serviced the boiler? It might be that they have adjusted one of the settings, perhaps speak to them?

 

[Chuck]

What could be the issue here?

You might be jumping the gun. At this time of year in the UK the house might not be cold enough to need more heat than is being supplied. At what temperature is the room with the thermostat in while this is happening?

Another possibility is weak circulation. Could be due to sludge, a failing or incorrectly set pump, a partially closed valve. Thermostatic radiator valves (TRVs) sometimes stick shut over the summer but you'd need this to have happened to several of them for this to be the cause.

 

[kilodelta]

kilodelta, did you manage to resolve this issue?

We have a Vaillant system boiler, and had it serviced last month. With the heating now required in the mornings, we've realised that the radiators don't warm up fast enough.

Our boiler temperature is set at 70 degrees, and last year, as soon as heating (or hot water) was required, it would fire the boiler to 70 degrees instantly, to warm up the entire house rapidly. Since the service, it's heating up slowly.

I have checked the boiler temperature and it goes from 20 degrees (when off) to around 40 degrees for 10-15minutes, then takes a break (radiator symbol flashing) for around 10 minutes. It then fires up again and takes the temperature to 65-70 degrees, but it takes at least 30 minutes, whereas previously it used to be instant.

What could be the issue here?

@Amz84uk Did you manage to solve the issue? It’s getting cooler and the issue is more noticeable.

 

[John.g]

kilodelta, did you manage to resolve this issue?

We have a Vaillant system boiler, and had it serviced last month. With the heating now required in the mornings, we've realised that the radiators don't warm up fast enough.

Our boiler temperature is set at 70 degrees, and last year, as soon as heating (or hot water) was required, it would fire the boiler to 70 degrees instantly, to warm up the entire house rapidly. Since the service, it's heating up slowly.

I have checked the boiler temperature and it goes from 20 degrees (when off) to around 40 degrees for 10-15minutes, then takes a break (radiator symbol flashing) for around 10 minutes. It then fires up again and takes the temperature to 65-70 degrees, but it takes at least 30 minutes, whereas previously it used to be instant.

What could be the issue here?

I think your boiler is, on fire up, probably exceeding the setpoint temp by 5C, SP+5cC, 75C in your case with burner cut off, it will the stay off until the anti cycle time has elapsed and repeat.

Do you know how to read the d parameters??.
What model Vaillant do you have?.

 

[kilodelta]

@John.g This is exactly what's happening. It gets to exactly +5C, cuts off, and then the anti cycle time comes on again. I have an ecoFIT Pure 630 system boiler.

I don't know what d parameters are but I can look up how to read them. Is this something I can possibly fix myself or should I call a Valliant approved engineer?

 

[John.g]

You can look at these and change, if required, page 13 of the attached, suggest you have a look and note the following parameters, page 28, and post back.

d.00 Heating maximum output kw
d.02 Maximum burner anticycling time in heating mode. mins

 

[Chuck]

@John.g This is exactly what's happening. It gets to exactly +5C, cuts off, and then the anti cycle time comes on again.

That's the boiler behaving correctly in circumstances were there is insufficient circulation/emission by the radiator system to carry the heat away from the boiler. If it's started happening after years of okay operation, it's likely to be because some of the TRV's have stuck shut during the summer, or someone has turned down TRV's to save energy so the radiator system is not dissipating heat, or an automatic bypass valve is passing when it shouldn't be. Could also be a weak or failing pump. It is very unlikely to be because the boiler parameters need changing, which is a last resort and should only be attempted by people who know what they are doing, have ruled out other causes and, preferably, have consulted the manufacturer's tech support.

 

[kilodelta]

Thanks. I brought up the installer menu and it asks for a code. Do I need to enter the value “17” in order to check the diagnostics code? I’d prefer a read only menu so I don’t screw anything up.

When the boiler engineer did the annual check last year he did the service but we’ve always had low gas pressure. Like every time a gas safe engineer comes by they called Cadent. This time, there was a team in the area and they move the gas meter outside and fixed the problem that day.

I started noticing the 5C cycle issue in the next couple of weeks. Could the service and/or gas pressure issue be the cause of issue? I called the engineer and he said it was normal, as above.

Should I open all the TRVs to full heat? I did dial them back.

 

[John.g]

I think so yes, 17 is the passcode, you can then just look at the appropriate parameters without changing anything.
If the 5C cycle issue is coming up while the boiler is firing for > a few minutes then the heating demand is lower than the minimum boiler output and it will cycle. (normal)

 

[Deleted member 120897]

Yes 17 is the installer code.

 

[kilodelta]

You can look at these and change, if required, page 13 of the attached, suggest you have a look and note the following parameters, page 28, and post back.

d.00 Heating maximum output kw
d.02 Maximum burner anticycling time in heating mode. mins

D.000 = 30kw
D.002 = 20 minutes

 

[John.g]

You have 7 rads?, so a max output of ~ 14kw, d.00 should be reduced to say 16kw IMO.
The 20 min anticycle setting is a actual time of 4.5 minutes with a SP temperature of 65C so probably OK.