Vaillant Ecotec Plus - Luke warm water

[Daljit]

Hi

Ecotec Plus 831 HW only luke warm, CH working fine. When running HW, flow pipes do not get warm. Diverter valve has been replaced (probably unnecessarily).

When running HW, burner starts, temperature rises few degrees above setting then burner cuts out, temp falls then burner continues on this on/off cycle. The water doesn’t reach the setting (50 degrees) only lukewarm.

Any ideas?

Cheers, Daljit

 

[Deleted member 267285]

Is this the one with the blue lcd display?

 

[Daljit]

Not the blue display model

 

[Johntheo5]

Hi

Ecotec Plus 831 HW only luke warm, CH working fine. When running HW, flow pipes do not get warm. Diverter valve has been replaced (probably unnecessarily).

When running HW, burner starts, temperature rises few degrees above setting then burner cuts out, temp falls then burner continues on this on/off cycle. The water doesn’t reach the setting (50 degrees) only lukewarm.

Any ideas?

Cheers, Daljit

You say the burner cuts out when the temperature rises a few degrees above setting, if you are talking about the DHW temperature then the burner will cut out at the SP+5C or 55C, this shouldnt happen unless the DHW flowrate is very low, possibly around 2.5LPM or so.

 

[Deleted member 267285]

The hot water temperature seems low. Could be blocked plate and or canoe filter too.

 

[Daljit]

You say the burner cuts out when the temperature rises a few degrees above setting, if you are talking about the DHW temperature then the burner will cut out at the SP+5C or 55C, this shouldnt happen unless the DHW flowrate is very low, possibly around 2.5LPM or so.

Hi

Just ran it to measure flow rate - it’s approx 8.5l/min. The burner stayed on but water was tepid although display fluctuated between 54-61 degrees.

 

[Daljit]

The hot water temperature seems low. Could be blocked plate and or canoe filter too.

Hi

CH working fine. Just set rads to 55 degrees and boiler operating constantly at 57 for 6-7mins now. Rads are fairly hot to touch too, definitely close to desired temp.

Makes me think not a blocked plate then?

So more likely canoe filter?

 

[Deleted member 267285]

Hi

CH working fine. Just set rads to 55 degrees and boiler operating constantly at 57 for 6-7mins now. Rads are fairly hot to touch too, definitely close to desired temp.

Makes me think not a blocked plate then?

So more likely canoe filter?

I didn’t mention the rads. Check the hot water dial, the one above the rads setting.

 

[Johntheo5]

Hi

CH working fine. Just set rads to 55 degrees and boiler operating constantly at 57 for 6-7mins now. Rads are fairly hot to touch too, definitely close to desired temp.

Makes me think not a blocked plate then?

So more likely canoe filter?

Is the canoe filter just on the primary flow pipe into the heat exchanger, a DHW flowrate of 8.5LPM and a mains temp of (mine, just now) 19C requires 24.91kw to give a flow temp of 61C (and 20.76kw to give 54C) so you are getting a fair whack of heat which doesn't point to a fouled heat exchanger and probably not a blocked canoe filter either?. Its possibly a faulty DHW sensor?.

Can you just run the flowrate at ~ 4.0LPM or so to see if the temp stays steady, also run it again at ~ 8.5LPM and note D.040 (primary flow temp) & D.041(primary return temp) also D.036.

 

[Daljit]

Is the canoe filter just on the primary flow pipe into the heat exchanger, a DHW flowrate of 8.5LPM and a mains temp of (mine, just now) 19C requires 24.91kw to give a flow temp of 61C (and 20.76kw to give 54C) so you are getting a fair whack of heat which doesn't point to a fouled heat exchanger and probably not a blocked canoe filter either?. Its possibly a faulty DHW sensor?.

Can you just run the flowrate at ~ 4.0LPM or so to see if the temp stays steady, also run it again at ~ 8.5LPM and note D.040 (primary flow temp) & D.041(primary return temp) also D.036.

Hi

Running at 4.5lpm when HW set at 50 degrees results in temp climbing to over 60, burner cutting out until temp falls, then repeats again and again. As described in OP.

Running at 8.5lpm, d.40 - 55-60, d.41 - 51, d.36 - 4.

Whether running at 4.5 or 8.5lpm, temp no where near 50 degrees. Probably around 20.

So, it does look like a faulty DHW sensor.

 

[Daljit]

I didn’t mention the rads. Check the hot water dial, the one above the rads setting.

Yip, dial appears to be working but no effect on output.

 

[Johntheo5]

Hi

Running at 4.5lpm when HW set at 50 degrees results in temp climbing to over 60, burner cutting out until temp falls, then repeats again and again. As described in OP.

Running at 8.5lpm, d.40 - 55-60, d.41 - 51, d.36 - 4.

Whether running at 4.5 or 8.5lpm, temp no where near 50 degrees. Probably around 20.

So, it does look like a faulty DHW sensor.

You said above that "The burner stayed on but water was tepid although display fluctuated between 54-61 degrees." I assumed this temperature was the DHW (apparent) temperature, the minimum output of the 831 is ~ 8.5kw so if it kept firing even at this minimum output the DHW temperature will still be over 33C. You might also look at D.004 which is the measured value of the HW sensor in deg.C. D.036 (Hot water flow quantity (impeller sensor) In l/min) is only reading 4.0LPM even though you measured the flow at ~ 8.5LPM, did you measure this at a mixer tap or shower/, just wondering if you have a problem with a mixer resulting in this very low 4.0LPM DHW flow which will just about satisfy the min output of 8.5kw.

 

[Daljit]

You said above that "The burner stayed on but water was tepid although display fluctuated between 54-61 degrees." I assumed this temperature was the DHW (apparent) temperature, the minimum output of the 831 is ~ 8.5kw so if it kept firing even at this minimum output the DHW temperature will still be over 33C. You might also look at D.004 which is the measured value of the HW sensor in deg.C. D.036 (Hot water flow quantity (impeller sensor) In l/min) is only reading 4.0LPM even though you measured the flow at ~ 8.5LPM, did you measure this at a mixer tap or shower/, just wondering if you have a problem with a mixer resulting in this very low 4.0LPM DHW flow which will just about satisfy the min output of 8.5kw.

Hi

Sorry, I don’t have a thermometer so can’t take actual reading. If a v hot bath is around 38-40 degrees, I estimate the DHW temperature being produced is below 30 degrees.

I measured flow of 8.5LPM at kitchen sink, 2.5m pipe run from boiler. D.36 reading is 4. D.04 is 42.

Kitchen tap is a mixer but pretty sure no fault.

Measured flow in bath (not a mixer). Got a whopping 16LPM but D.36 read 9. D.04 is 41. Water temperature definitely cooler than kitchen tap. Maybe 20-25 degrees.

Ran basin tap (not a mixer) but didn’t measure LPM. However, it’s faster than kitchen tap but less than bath. D.36 reading is 6. D.04 is 42.

Pipe work to bathroom from boiler starts 15mm then switches to 22mm about halfway.

 

[Johntheo5]

I measured flow of 8.5LPM at kitchen sink, 2.5m pipe run from boiler. D.36 reading is 4. D.04 is 42.
Kitchen tap is a mixer but pretty sure no fault.

Just assuming a mixer fault then 4.0LPM @ 42C + 4.5LPM @ 19C gives 8.5LPM @ 29.8C.

Just feel the DHW pipe where it exits the boiler, if that only feels 25C ish and D.04 is 42C then points to a DHW sensor problem?.

 

[Daljit]

Just assuming a mixer fault then 4.0LPM @ 42C + 4.5LPM @ 19C gives 8.5LPM @ 29.8C.

Just feel the DHW pipe where it exits the boiler, if that only feels 25C ish and D.04 is 42C then points to a DHW sensor problem?.

This is odd. The DHW at boiler is hot to touch, i.e. the 43 degrees D.04 reading being given is correct. If I grip the pipe it becomes uncomfortable after 5-7 secs.

However, 2.5m away, at the kitchen HW tap, the water’s lukewarm!

There’s a tee beneath the boiler leading to a WC, and closer to the sink, another tee to the bathroom. I’ve closed the WC basin’s HW isolator (it’s a mixer tap). This doesn’t make any difference to the temp of water from kitchen tap.

I’d isolate the mains CW at the kitchen tap but unfortunately there’s no isolator fitted. I’ll fit one later today - however, given above strongly suggests there is a fault with the kitchen mixer tap?

Also, faulty mixer tap in kitchen would explain why the D.36 readings don’t reflect the actual flow rates I’m measuring at the kitchen tap (8.5 LPM, D.04 is 4) or bath tap (16 LPM, D.0.04 is 9)?

Lastly, probably a separate issue. I notice if I isolate mains CW immediately beneath the combi, with a quarter turn using an Allen key, it doesn’t work. DHW at kitchen sink continues to flow.