Vaillant ecotec 438 short cycling

[noddy997]

Hi all, got a Vaillant Ecotec 438 since 2009 and I never noticed this but it seems to be cutting off or short cycling. Had new rads fitted recently and when the flow is at 70 the return is now a measly 35!! Prior to the rad change a 70 flow = 46 return.

There are 11 rads in the house in total, all except 3 are type 22 and some are 1.6m long and one is 2m and the others are 1.4 and 1m long.

A magnaclean was fitted and within a week it was full! A chemical flush was attempted today but engineer said it needs a power flush as there might be some blockages in the pipe that are causing the huge gap in return temp and the boiler cutting off.

The boiler reaches 70c and then cuts off and then kicks in again within a minute rather stay continuously on. What else could be the issue for this?


I have attached a video. Also the tapping noise is me holding the cover.

Many thanks.

 

[muggles]

These boilers are quite dirt sensitive. If the system was bad enough to fill a Magnaclean in a week it's quite likely it's got into the heat exchanger and blocked it. They can prove almost impossible to flush due to the design - often replacement is the only option.

 

[Johntheo5]

What make model mode setting and age is the circ pump, was the head removed and pump port and impeller vanes cleaned.

 

[noddy997]

What make model mode setting and age is the circ pump, was the head removed and pump port and impeller vanes cleaned.

It's the GRUNDFOS UPS3 15-50/65

I don't know if that is sufficient anymore though as the old rads were the non convector types from the 80s you could say, first gen type rads.

No it wasn't cleaned. The pump is always on the highest setting.

I have replaced the pump a few times in the last few years however...

 

[noddy997]

These boilers are quite dirt sensitive. If the system was bad enough to fill a Magnaclean in a week it's quite likely it's got into the heat exchanger and blocked it. They can prove almost impossible to flush due to the design - often replacement is the only option.

It was given a thorough service back in July, but obviously the heating wasn't used from then until now due to hot weather.

 

[Harry Bloomfield]

It was given a thorough service back in July,

A simple boiler service, will not include any work on the water circuit. Did your engineer today do a thorough flush through of the water circuits (pipes and radiators)?

The very rapid rise in flow temperature, suggests a poor flow through the boiler, which could be due to any part of the water circuit.

 

[Johntheo5]

It's the GRUNDFOS UPS3 15-50/65

I don't know if that is sufficient anymore though as the old rads were the non convector types from the 80s you could say, first gen type rads.

No it wasn't cleaned. The pump is always on the highest setting.

I have replaced the pump a few times in the last few years however...

Once the flow/return dT reaches 30C the boiler will recycle, the dT was allways pretty high even at 24C, its more than likely that the boiler HEX is at least partially blocked, that UPS3 should be powerful enough as its a high capacity pump.

If the boiler has a automatic bypass valve (ABV) check its setting and increase its index setting to 0.5 if not set there.

As a temporary measure you could reduce d.00 to say 15kw to see if the boiler can at least get away without reaching 30C, you can allways gradually increase it depending on the dT.

 

[noddy997]

A simple boiler service, will not include any work on the water circuit. Did your engineer today do a thorough flush through of the water circuits (pipes and radiators)?

The very rapid rise in flow temperature, suggests a poor flow through the boiler, which could be due to any part of the water circuit.

Yes he did but this was a chemical flush rather than a proper power flush. He used the adey flushing pump but that's not a power flush. He said he will return with the usual power flusher as pipes may be blocked, but if they're blocked the system would not run unless they're partially blocked?

 

[noddy997]

Once the flow/return dT reaches 30C the boiler will recycle, the dT was allways pretty high even at 24C, its more than likely that the boiler HEX is at least partially blocked, that UPS3 should be powerful enough as its a high capacity pump.

If the boiler has a automatic bypass valve (ABV) check its setting and increase its index setting to 0.5 if not set there.

As a temporary measure you could reduce d.00 to say 15kw to see if the boiler can at least get away without reaching 30C, you can allways gradually increase it depending on the dT.

How do I check and adjust the ABV?

Would lowering the d.00 cause it to run continuously / modulate rather than cut off and go through a full a cycle again and again as it does?

 

[Johntheo5]

How do I check and adjust the ABV?

It will look something like this and should be located fairly near the pump outlet . If you locate it just check the reading and post back before you adjust it.

Would lowering the d.00 cause it to run continuously / modulate rather than cut off and go through a full a cycle again and again as it does?

Don't know, just try it, after reducing it and firing up the boiler just watch d.40, if it exceeds the target temperature by 5C, then it will trip and do a anticycle. After reducing d.00 to 15kw and firing the boiler watch d.40 only and see what temperature it reaches.

 

[noddy997]

It will look something like this and should be located fairly near the pump outlet . If you locate it just check the reading and post back before you adjust it.

View attachment 317343

Don't know, just try it, after reducing it and firing up the boiler just watch d.40, if it exceeds the target temperature by 5C, then it will trip and do a anticycle. After reducing d.00 to 15kw and firing the boiler watch d.40 only and see what temperature it reaches.

I don't have one of them. How do I set the d.00? I can adjust it but can't seem to set it, it just flashes and no matter what I press it doesn't set it and then reverts back to 38 (kw)

 

[Johntheo5]

Afraid I dont know as not familiar with these boilers.

 

[noddy997]

Afraid I dont know as not familiar with these boilers.

I set it at 20kw. It didn't cut off, and then decided to see how much further I can increase it, it was fine at 24 too and at 28 it cut off again.

I then reduced it to 22, 16 and even 20 and its cutting off again!

 

[Johntheo5]

Presume you did this? someone just told me.
"to change d.0 to the chosen value, they need to press the ‘I’ button for 5 secs which will then store the value"

reduce it right down to its minimum, say 8kw but I doubt if it will help because the boiler fires up at ~ 65% of its max output for up to 60 secs, so fires up at ~24kw and would require around a flowrate of 14LPM to keep the flow/return dT below 25C.
Watch d.40 as soon as it fires up.
There should really be a ABV on the system which would help.

 

[noddy997]

Presume you did this? someone just told me.
"to change d.0 to the chosen value, they need to press the ‘I’ button for 5 secs which will then store the value"

reduce it right down to its minimum, say 8kw but I doubt if it will help because the boiler fires up at ~ 65% of its max output for up to 60 secs, so fires up at ~24kw and would require around a flowrate of 14LPM to keep the flow/return dT below 25C.
Watch d.40 as soon as it fires up.
There should really be a ABV on the system which would help.

But is 8kw sufficient? The rads alone are 5kw type 22 and its a big old detached house with extensions and a lot of pipework?

Yes I did the above. Thank you