Evening All,
Hoping some plumbing/heating engineers/other knowledgable folk on here might be able to assist with some questions about my new boiler.
We had the new Viessmann 200-W 35kw Combi installed this week by a Viessmann registered local heating engineer. It's the new 2019 version with the increased 17 litre per minute DHW flow rate and the larger screen on the front. Very recently released or so I'm told. It replaced a 14 year old Vaillant Ecotec 831 Combi which was beginning to have issues. We had hoped that a newer boiler would give us better hot water flow rates and lower gas bills. Have been told by multiple people that Viessmann are the brand to go for these days.
We didn't get off the to the best start when it was installed, turned on and promptly died. Viessmann themselves had to come out 2 days later (meanwhile no heating or hot water - not brill with 2 young kids) and replaced 3 internal boards including the front panel. Problem solved, but with it being a brand new model there was lots of head scratching and phone calls back to technical department.
It's wired into our existing Honeywell Evohome system which has 12 zones with all radiators on the wireless TRV's. We have a towel rail in the bathroom with no TRV and that's permanently open which I think needs to be the case to allow the boiler to circulate when the TRV's close themselves off. Because of this, the boiler runs in 'continuous' mode rather than weather comp or whatever the other option are.
Seems to be working OK now, BUT:
1) We couldn't get water hotter than 41c out of the bath hot tap. Boiler set to 60 degrees. I filled a bucket and timed it, the flow was 17 litres per minute or just over but the incoming main temperature is about 11 degrees. The boiler is rated at 17l/m, but is this a certain number of degrees over the incoming temp (i.e. if that's 17l/m at a 30c raise, should this be about what we would expect?) The plumber thought that the boiler should limit hot water flow to what it is able to heat to the set temp, so either this is not the case or it's not working properly. Either way, with a screwdriver I reduced the flow into the boiler on the inlet valve underneath it until (with the bath hot tap on full and monitoring the boiler display) the set temp could be met (we get 10-11l/m now at 60 degrees so a small improvement on the previous boiler which I measured at 9.1l/m before it went). I had hoped for better, but couldn't find a graph/table anywhere showing what litres per minute should be achievable at a particular incoming mains water temp?
2) Seems to take much longer than the old boiler to start producing hot water. We seem to have to drain off quite a bit now before it runs hot, this was not the case before so the pipe run shouldn't have anything to do with it (and it was a straight swap). I notice the heating settings on the boiler have "Normal Flow" and "Reduced Flow". I assume normal flow is the temperature of the boiler when the heating is on, and reduce when there is no heat being called for. These were 70 degrees and 20 degrees respectively. Would increasing the reduced flow temperature likely have any bearing on the speed of DHW production? The boiler seems to ramp up fairly slowly - it sounds like a jet engine being throttled up gradually! I can't see any mention of an 'eco' mode or anything either.
Many thanks in advance for any thoughts on the above!
ST.
Hoping some plumbing/heating engineers/other knowledgable folk on here might be able to assist with some questions about my new boiler.
We had the new Viessmann 200-W 35kw Combi installed this week by a Viessmann registered local heating engineer. It's the new 2019 version with the increased 17 litre per minute DHW flow rate and the larger screen on the front. Very recently released or so I'm told. It replaced a 14 year old Vaillant Ecotec 831 Combi which was beginning to have issues. We had hoped that a newer boiler would give us better hot water flow rates and lower gas bills. Have been told by multiple people that Viessmann are the brand to go for these days.
We didn't get off the to the best start when it was installed, turned on and promptly died. Viessmann themselves had to come out 2 days later (meanwhile no heating or hot water - not brill with 2 young kids) and replaced 3 internal boards including the front panel. Problem solved, but with it being a brand new model there was lots of head scratching and phone calls back to technical department.
It's wired into our existing Honeywell Evohome system which has 12 zones with all radiators on the wireless TRV's. We have a towel rail in the bathroom with no TRV and that's permanently open which I think needs to be the case to allow the boiler to circulate when the TRV's close themselves off. Because of this, the boiler runs in 'continuous' mode rather than weather comp or whatever the other option are.
Seems to be working OK now, BUT:
1) We couldn't get water hotter than 41c out of the bath hot tap. Boiler set to 60 degrees. I filled a bucket and timed it, the flow was 17 litres per minute or just over but the incoming main temperature is about 11 degrees. The boiler is rated at 17l/m, but is this a certain number of degrees over the incoming temp (i.e. if that's 17l/m at a 30c raise, should this be about what we would expect?) The plumber thought that the boiler should limit hot water flow to what it is able to heat to the set temp, so either this is not the case or it's not working properly. Either way, with a screwdriver I reduced the flow into the boiler on the inlet valve underneath it until (with the bath hot tap on full and monitoring the boiler display) the set temp could be met (we get 10-11l/m now at 60 degrees so a small improvement on the previous boiler which I measured at 9.1l/m before it went). I had hoped for better, but couldn't find a graph/table anywhere showing what litres per minute should be achievable at a particular incoming mains water temp?
2) Seems to take much longer than the old boiler to start producing hot water. We seem to have to drain off quite a bit now before it runs hot, this was not the case before so the pipe run shouldn't have anything to do with it (and it was a straight swap). I notice the heating settings on the boiler have "Normal Flow" and "Reduced Flow". I assume normal flow is the temperature of the boiler when the heating is on, and reduce when there is no heat being called for. These were 70 degrees and 20 degrees respectively. Would increasing the reduced flow temperature likely have any bearing on the speed of DHW production? The boiler seems to ramp up fairly slowly - it sounds like a jet engine being throttled up gradually! I can't see any mention of an 'eco' mode or anything either.
Many thanks in advance for any thoughts on the above!
ST.
