Any Boiler Engineers? (New combo boiler)

Converge · 12 Nov 2019 at 19:20

Hi all,

I’ve just had a new combi boiler installed (Viessmann 050-W) and, apart from not really trusting the installer much, it seems to be exhibiting weird behaviour since installation in the last couple of weeks.
Whenever the heating is on/has been on recently, and you use a tap for hot water, it comes out at the radiator temperature (70c) rather than near about the tap temperature (52c). It takes over a minute to come down to any semblance of a reasonable temperature, let alone 52c.
I’ve never noticed this behaviour with other boilers of mine or friends.
Is this a incorrect installation? Shouldn’t there be a separate flow or control to stop it scalding people?

Also, with having a Nest Thermostat and radiators with TVRs, should I have the TVRs set at max like the installer left them at, and leave it to the Nest to control temperature, or change them (ie bedroom a bit cooler)

Any help would be great!

The_One · 12 Nov 2019 at 19:28

Ask 200sols from the other combi thread hes a non qualified expert

LuckyBenski · 12 Nov 2019 at 19:29

Regarding the last point, let the nest do its job if you have thermostats/control in each room. How does the Nest regulate each room separately?

In terms of the DHW (hot water) supply, that's not right at all. The boiler should have separate settings for each temperature (DHW and central heating). The maximum possible for CH is usually around 85-90 whereas for DHW is 65-70. So even if setting everything up max, you shouldn't be seeing that. Reading the boiler's manual should help but really, you should call the engineer back in. I had a new boiler last Thursday and on the evening dropped him a line to say the remote control didn't appear to be triggering the boiler. Sorted by the next evening.

Is it possible he's crossed the two systems over internally? Well, swapped them. Are the radiators getting up to temp and flowing?

200sols · 12 Nov 2019 at 19:29

The_One said:
Ask 200sols from the other combi thread hes a non qualified expert

Haha, I was half expecting this post. Do grow up mate.

android-fan · 12 Nov 2019 at 19:37

My Baxi behaves similarly, when I queried it with the fitter I was told it was normal and in fact a positive in that you get immediate hot water if the heating is running already. Obviously the downside if you don't have a mixer tap is getting burnt.

Converge · 12 Nov 2019 at 20:11

LuckyBenski said:
Regarding the last point, let the nest do its job if you have thermostats/control in each room. How does the Nest regulate each room separately?

In terms of the DHW (hot water) supply, that's not right at all. The boiler should have separate settings for each temperature (DHW and central heating). The maximum possible for CH is usually around 85-90 whereas for DHW is 65-70. So even if setting everything up max, you shouldn't be seeing that. Reading the boiler's manual should help but really, you should call the engineer back in. I had a new boiler last Thursday and on the evening dropped him a line to say the remote control didn't appear to be triggering the boiler. Sorted by the next evening.

Is it possible he's crossed the two systems over internally? Well, swapped them. Are the radiators getting up to temp and flowing?

Cheers guys for the quick replies

Additional info about the Nest bit, the room that is coldest is my lounge, but it is the radiator closest to the boiler, so it doesn’t have a TRV. So the other rooms have generally heated up by the time the thermostat sets the boiler to off but my lounge is still cold. So I was thinking perhaps have the TRVs lower in the thermostat area so that it heats for longer!

I can set DHW and Rad temps separately. Radiator is at 70c and DHW is at 52c.
It just seems markedly hotter when using taps (without mixers) to the point of whipping your hands away from the water. Just seems odd to me that it doesn’t come out at the tap/DHW temp through a separate feed.

I replaced my Baxi DuoTech with this Viessmann, and perhaps the Baxi was just not very efficient so I never got scalded!

DXP55 · 12 Nov 2019 at 20:37

Had my Oil fired combi serviced today and when he was checking it out he turned stats up on boiler - rads were so hot I couldn't touch them - same with hot water - when he finished I turned stats down to 2 (1-5) - I always set my stats so I can just keep my hands on rad - same goes with water - If like mine your boiler should have a 5lt hot water tank built in - the boiler automatically keeps this hot all the time so when you turn on tap you don't have to wait for it to get hot. Just play with the boiler stat settings.

LuckyBenski · 12 Nov 2019 at 20:37

Converge said:
I replaced my Baxi DuoTech with this Viessmann, and perhaps the Baxi was just not very efficient so I never got scalded!

I think this'll be the case. My hot water was never too hot to touch even set to max. New boiler is 5° below its max and it's nice and toasty!

The CH and DHW must be on separate feeds - you're not seeing the grimy treated radiator water coming out of taps are you? But something isn't right.

Converge · 12 Nov 2019 at 20:53

DXP55 said:
Had my Oil fired combi serviced today and when he was checking it out he turned stats up on boiler - rads were so hot I couldn't touch them - same with hot water - when he finished I turned stats down to 2 (1-5) - I always set my stats so I can just keep my hands on rad - same goes with water - If like mine your boiler should have a 5lt hot water tank built in - the boiler automatically keeps this hot all the time so when you turn on tap you don't have to wait for it to get hot. Just play with the boiler stat settings.

There's nothing to play with to be honest, there's a DHW setting and a Rad setting, and the SERV setting for the engineer. So i'm not sure what else I could do!

LuckyBenski said:
I think this'll be the case. My hot water was never too hot to touch even set to max. New boiler is 5° below its max and it's nice and toasty!

The CH and DHW must be on separate feeds - you're not seeing the grimy treated radiator water coming out of taps are you? But something isn't right.

No, the water is clean, so it doesn't seem to be that. And i get direct cold water too. Maybe i'm worrying about nothing, it's just the engineer was in a rush by the time he got around to installing it due to delivery delays and actually didn't even hang the boiler properly, so he's having to come back and sort that seperately. Hence my reluctance to take his word for it!

LuckyBenski · 12 Nov 2019 at 21:34

Converge said:
No, the water is clean, so it doesn't seem to be that. And i get direct cold water too. Maybe i'm worrying about nothing, it's just the engineer was in a rush by the time he got around to installing it due to delivery delays and actually didn't even hang the boiler properly, so he's having to come back and sort that seperately. Hence my reluctance to take his word for it!

Good opportunity to let him know if anything else is up though. Have you got time to buy a thermometer and check the water temp?

Hedge · 12 Nov 2019 at 21:59

Turn the thermostat down to its lowest and see if temp is lower.

£15 · 13 Nov 2019 at 20:53

Does it have a water pre-heat, or eco function? I had a quick Google of the model and one product sheet mentioned an instantaneous water heater?

Is it the boiler keeping a small amount of preheated water ready and waiting so you don't have to wait for it to heat up?

FlyingFish · 13 Nov 2019 at 21:42

BadMojo said:
Does it have a water pre-heat, or eco function? I had a quick Google of the model and one product sheet mentioned an instantaneous water heater?

Is it the boiler keeping a small amount of preheated water ready and waiting so you don't have to wait for it to heat up?

Ding Ding! We have a winner

And the preheat is from the ch