Combi vs tank - which should I go for?

[SJB060685]

Good modulation is paramount and no other gas boiler manufacturer on the market comes close to Viessmann modulation. Poor modulation means a lot more cycles at the boiler when the outside temperature is not design temperature. This puts a lot of wear and tear on burner components and obviously not as efficient. A Viessmann cylinder will come with everything needed to plug into the boiler a run along nicely but you could choose another cylinder brand if you wanted to.
The Viessmann is already built for a 4 pipe set up with an internal diverter valve so PDHW is easily achieved. That valve can function as a one port outlet though if running new pipes to the cylinder is not possible and you have use external valves.
Vaillant are good boilers but in my opinion nothing comes close to Viessmann. That is just my opinion though.

 

[b21playa]

Good modulation is paramount and no other gas boiler manufacturer on the market comes close to Viessmann modulation. Poor modulation means a lot more cycles at the boiler when the outside temperature is not design temperature. This puts a lot of wear and tear on burner components and obviously not as efficient. A Viessmann cylinder will come with everything needed to plug into the boiler a run along nicely but you could choose another cylinder brand if you wanted to.
The Viessmann is already built for a 4 pipe set up with an internal diverter valve so PDHW is easily achieved. That valve can function as a one port outlet though if running new pipes to the cylinder is not possible and you have use external valves.
Vaillant are good boilers but in my opinion nothing comes close to Viessmann. That is just my opinion though.

Thanks, I’ll look into these.

Wonder why their standard warranty is only 3yrs, would need their trained installer to get the 5/10/12years

 

[SJB060685]

I believe non Viessmann trained installers only qualify you for a 3 year warranty. A Viessmann trained installer qualifies you for 5 years I think and I think there’s a chargeable upgrade to 10-12 years warranty if installed by a Viessmann installer depending on your boiler model.

 

[hometech]

Good modulation is paramount and no other gas boiler manufacturer on the market comes close to Viessmann modulation. Poor modulation means a lot more cycles at the boiler when the outside temperature is not design temperature. This puts a lot of wear and tear on burner components and obviously not as efficient. A Viessmann cylinder will come with everything needed to plug into the boiler a run along nicely but you could choose another cylinder brand if you wanted to.
The Viessmann is already built for a 4 pipe set up with an internal diverter valve so PDHW is easily achieved. That valve can function as a one port outlet though if running new pipes to the cylinder is not possible and you have use external valves.
Vaillant are good boilers but in my opinion nothing comes close to Viessmann. That is just my opinion though.

If my heat demand is average 15kw and max is 22 kw and I have a boiler that is 24kw, how much modulation do I need?
just out of interest, if viesman is so perfect, why does it represent such an insignificant percentage of the sales in the UK?
Combis heat water or they heat the circuit, they can't do both simultaneously. A system boiler 4 pipe system works the same way as the combi, the heat is directed between circuits.
Having separate devices for specific jobs is the most efficient and cost effective way forward.
Storing water that you have heated to then keep hot and then mix down because its too hot to use directly..that's just silly....how on earth can that ever be considered good practice? its just wasteful..
We live in the 21st now, not the 19th.....

 

[SJB060685]

I never said Viessmann were perfect, I simply pointed out a few things as to why they’re considered superior by many and I did state that it was just my opinion, although I have many associates who feel the same.
I have my views and so do you and whether you agree or disagree with me I respect yours. I’m not going to get into a debate with you as I’ve seen some of your contributions in the past cause confusion and ultimately the conversation goes nowhere.
I will keep my mouth shut on this thread now.

 

[b21playa]

Just fit the combo valve eg prv at your mains stop tap or a secondary pressure reducer to keep the whole system at the same pressure

First thing to do is get a heat loss done then you know the load of the new boiler

Hi Shaun

I’ve got a new mains being fitted beginning of March. I’ve asked for 32mm which will terminate in the garage. I’ll do a temp connection to the existing in 22mm pex which I already have but ultimately it needs to feed to cupboard where new tank will be. This will need to run under the floorboards, can this be done in 28mm pex/pb pipe?

Many thanks

 

[ShaunCorbs]

Yes as your running plastic it’s best to upsize like you’ve done eg 22mm copper 28mm plastic / pex

 

[b21playa]

Yes as your running plastic it’s best to upsize like you’ve done eg 22mm copper 28mm plastic / pex

That’s great.

Water main guy recommended 25mm so as not to reduce pressure but as prv is 3bar I thought it was ok to move to 32mm
I had read 28mm has the same internal diameter as 32mm mdpe so thought best to run this all the way to the prv location. Just need to decide on pex or polybutylene pipe.

The 28mm plastic will terminate to a stopcock and then run internally for a short distance in 22mm copper to the prv

 

[ShaunCorbs]

Yes fine to move upto 32mm

Yes 28mm copper is same dia internally as 32mm alk