combination boiler

pool fan

hi

im converting my garage into a granny flat,im putting in a combination boiler for the heating and hot water as i dont hae room for a cylinder.My problem is that i hae very poor mains pressure,can i put a tank outside with a grundfos pump on it to supply the cold feed for the Dhw water through the combi boiler.

thanks

I doubt it, although there are lots of installations that pump the mains without fitting a break tank, but now all gas boiler installations must be fitted to manufactures instructions to meet Irish standards(regs), i do not know of any manufacturers that allow there combis to be pump fed, you could try looking at a accumulator http://www.hvnplus.co.uk/page.cfm/action=Archive/ArchiveID=6/EntryID=103
this can improve flow rates but may not be any good for improving pressure, Gary

f1_jb

There no problem putting a pump on most combi boilers, they all have a max pressure rating on them I know that on a Vokera it's 6bar max and I'm sure most other boilers are the same.

The most important thing you need to watch is the flow rate trough the boiler it needs to be set with a flow cup if there is too much then you won't get the temperature rise and water will not be hot enough.

I'm a boiler manufactures engineer and you wouldn't be able to do it with the boilers i work on and meet the regs, now lots of people fit them with break tanks and they work but some don,t causing at times the boiler to over heat or the temp at the tap to spike, they don't meet is813, which may or not be a problem depending on the RGII engineer putting his name to it, the main problem is as a combi, technically they should be able to provide constant hot water and no break tank is big enough to do that, unlike a cylinder where you know how much water will be used till the hot water runs out and you size the break tank accordingly, now without me sounding like a big girls blouse i would say as a gas fitter what you want to do is easily doable as the hot water usage for your granny flat should be quite small, but as a manufactures engineer i couldn't sign off on that installation, so it's all down to how hard these new inspectors from RGII are going to be as they will have the final say, Gary.

f1_jb

Once the flow rate is set right then there isn't a problem, the max flow rate you will get is around 14ltr per minute, it would want to be a very poor water main feed not to keep a break tank full if the flow rate is set right.

Carlow52

I am of the opinion that no LA will allow u connect a combi boiler, or any pump for that matter, to the rising main.

My understanding is that you are allowed one outlet at the kitchen sink and another for the cold water tank.

This thread suggests otherwise.

In passing, what is a break tank please?

Carlow52

Carlow52 wrote: »

I am of the opinion that no LA will allow u connect a combi boiler, or any pump for that matter, to the rising main.

My understanding is that you are allowed one outlet at the kitchen sink and another for the cold water tank.
quote]

You are right but there are lots of propertys in Dublin that have pumped main supply's, unfortunately nobody is enforcing the regs.

A break tank is a calculated store of water for a property fed by mains then drawn from by a pump with the idea of supplying sufficient hot and cold water at a improved pressure and flow rate for the property's needs before the store empties, it is used when the mains is insufficient for the purpose.

Going back to the original post i may have to eat some humble pie, as what i have written is correct for my own products, you may find it's more possible than i thought, have a look at http://www.pumpexpress.co.uk/pump_ex_whole_house_boosting.htm, I'm going to shut up now, Gary.

bigbru

From reading all the brochures for combi boilers, the main selling points are:
- high efficiency
- instant hot water
- no need for a hot water cylinder
- no need for a cold water tank in the attic

It seems that all cold taps and the boiler are mains-fed, and the hot taps are all serviced by the boiler with direct hot water.
This seems to be a very efficient set up, and a small rad can be put in the hot-press to heat it, and there is more room due to the cylinder being removed.
Am I wrong in the impression I got?

JIMMYBOND007

This lad is right taps and boiler are connected to mains,you do need good mains pressure and last you need it commissioned,unless you are oftec reg or rgi reg you cant commission it.oil or gas?
if your rgi you should have your i.s813 in your van at all times,so look it up?if your oftec look at your oftec 1-4folder procedures.
competent person(s)=persons having the ability ,appropriate training,knowledge and experience to carry out the work been undertaken in a safe and proper manner.
installed as per manufactors instructions.