Calling all Remeha experts.

[D_Hailsham]

I had a Remeha 18V installed just over a year ago and it has behaved impeccably. However it sometimes does strange things.

The one which I can't understand is when it turns off and you see a 5 appearing (I have changed the display so that it shows the operation state rather than just one or two dots.)

According to the manual a 5 means:

a control stop from 3 till 10 minutes and appears if the set flow temperature (t1) has already been reached and the heating demand still exists.

Last night I happened to check the boiler temperatures etc via the control panel. The flow showed 70C, return 55C and the output was at maximum. The boiler then stopped and a 5 appeared. The flow temp started to drop and, within less than a minute, was down to about 35C.

What I can't understand is why the boiler didn't just modulate down to maintain the required flow temp instead of turning off.

I know it wasn't the room stat turning the boiler off as that would produce a code 6 - pump overrun.

Has anyone else come across this or can someone give an explanation for this behaviour? It doesn't seem logical.

 

[Agile]

This is what I would call an anticycling delay status.

It should occur when the flow reaches the set temperature and the boiler cannot modulate any lower.

Tony

 

[mickyg]

not sure about remehas specifically but sounds like you have poor circulation

 

[D_Hailsham]

It should occur when the flow reaches the set temperature and the boiler cannot modulate any lower.

I could understand that happening; but it went into the delay mode when the boiler was at max output.

not sure about remehas specifically but sounds like you have poor circulation

But if that was the case, shouldn't the boiler modulate down before switching off?

I'll monitor a bit more and see if it happens again.

 

[mickyg]

not sure about remehas specifically but sounds like you have poor circulation

But if that was the case, shouldn't the boiler modulate down before switching off?

I'll monitor a bit more and see if it happens again.

No not always, most boilers modulation profile is based on factors the software assumes about the system ie that there is a suitable flow rate through the heat exchanger and enough heat absorption to take away the heat. If the flow rate is too low the boiler can ramp up and hit a point of no return before it has decided to modulate down and thus shuts off/cycles.

Another explanation is that you caught it just as it had shut down whilst heating the water and the ch zone valve opened thus taking away all the heat in the pipework but that would be very coincidental !

 

[D_Hailsham]

No not always, most boilers modulation profile is based on factors the software assumes about the system ie that there is a suitable flow rate through the heat exchanger and enough heat absorption to take away the heat. If the flow rate is too low the boiler can ramp up and hit a point of no return before it has decided to modulate down and thus shuts off/cycles.

That situation would be covered by a code 9!

Code 9 is a lock-out and appears if the maximum temperature rise is exceeded or if the dT between the supply and return temperature ≥ 22°C or a rate of rise in the flow temperature > 2,7°C/sec. and also at a boiler-start with no through flow or insufficient water. The boiler will try to restart after 10 minutes.

Another explanation is that you caught it just as it had shut down whilst heating the water and the ch zone valve opened thus taking away all the heat in the pipework but that would be very coincidental !

I've a Y plan, so that situation would never arise.

 

[mickyg]

It may not have been a big enough difference to trigger the fault 9. In any case boilers don't always act as they should according to the manual !
Poor circulation on most glowworm boilers gives a fault code which says NTC defective, replace ntc, check harness to ntc !
Im gonna stick with poor circulation keep us posted

 

[Agile]

It should occur when the flow reaches the set temperature and the boiler cannot modulate any lower.

I could understand that happening; but it went into the delay mode when the boiler was at max output.


I'll monitor a bit more and see if it happens again.

There are time constants built into the software and particularly in respect of the flow temp monitoring. NTCs usually take a minute or two to respond. That's a long time in respect of temperature rise.

I still expect its just reacting appropriately for when the max heat output is high compared with the absorption of the heat load.

Tony

 

[Boilerman2]

The only time I have seen a Blocking code "9" on an Avanta has been due to low system pressure

The Return Temp was stated as being 55'c the NTC sensors work together to calculate required firing rate, however if your circulation is poor, the flow sensor will quickly reach the upper limit and force the burner off and cause the control stop function

You haven't said what the Set Temperature is (P.1) ?

 

[Agile]

In any case, you know that we would want to know the flow and return temperatures at the point it switches off!

Tony

 

[D_Hailsham]

I had a chance to check what was happening when the Head Cook was at Tesco's. The situation was not exactly the same as in my original query as the house was already up to temperature (21C), but I tried to simulate the conditions by setting the Target temperature to 24C.

P1 on the boiler is set to 72C

Immediately before the boiler lit the flow temp was 35C and the return 34C.
On lighting the boiler went immediately to Minimum output.
It took about 10 minutes to reach Max output. The flow was then 49C and return 30C
The flow continued to rise, taking another 20 minutes to reach 72C with a return of 58C
The flow temp stayed at 72 C, but the return rose above 58C.
The boiler throttled back but the return continued to rise, so it throttled back some more.
Eventually it stabilized with a flow of 72C and return of 62C.

Unfortunately the Head Cook returned with the shopping and complained about the heat, so I had to abandon the experiment.

Nevertheless, everything seems to check out and I couldn't see any sign of poor circulation. If anything it was too fast as it took 23 minutes for the flow temp to rise 23C when the boiler was at max power, which is 1C per minute. The boiler stops with a code 9 if the rate exceeds 2.7C per second!!

The pump (Grundfos 15/50) is on 3 at the moment. I might drop it to 2 and see what the effect is.

 

[CBF]

where is the pump wired to ?

 

[D_Hailsham]

where is the pump wired to ?

The boiler, so pump overrun can work - which it does.

 

[David937]

I don't know about your Remeha but my VRC430f does something exactly like this, it is not anticycling. It is described as:

'If the flow target temperature is achieved for a longer period of time, the heating is switched off for the prescribed pump blocking time (depends on the external temperature)'

I notice it happens when it is milder outside, say the controller asks for a flow temperature of 55ºc, the boiler will reach 55ºc, if it stays at 55ºc for a long time (longer than the controller 'thinks' it needs to reach the target temperature), the burner turns off and the pump continues to run for the 'pump blocking time' and then the burner comes on again. I believe it is to reduce the likelihood of overshoot, a lot of the time when the burner is off and its in the 'pump blocking time' the target temperature is reached so it won't come on again.

Anti-cycling only happens when it is actually switched off by the controller or when it can't maintain a set flow temperature even at the lowest output - it allows the flow temperature to go 5ºc above the target but if it still continues to rise it will go into anti-cycling.

 

[D_Hailsham]

'If the flow target temperature is achieved for a longer period of time, the heating is switched off for the prescribed pump blocking time (depends on the external temperature)'

I don't know if it was lost in translation in your manual, but the description in the later VRC470F says:

To save energy, you can set the pump blocking time during which the heating circuit pump remains deactivated. For each heating circuit, the controller checks if the measured flow temperature is 2 K above the calculated target value. If this is the case for 15 minutes, the pump of the heating circuit in question is deactivated for the set blocking time. The mixer remains in its current position. The blocking time set is reduced as a function of the outside temperature.

That would explain why is is called the "Pump Blocking Time" !!