Moving from traditional boiler to combi, do you leave the pipeworks in the loft?

[groovybug]

Hi everyone,

We are considering of changing our traditional boiler (hot water cylinder/water tank) to combi boiler to save up some space. At the moment, the water storage tank, heating system tank and all the pipeworks are in the loft, even the main cold water goes up to the loft before going down to taps (the boiler and water cylinder is in the kitchen).

Is it best to leave all the pipeworks here and reroute a few when converting (as obviously it will save a ton of work), or it is best to completely redo the plumbing and run the pipes under the bathroom/kitchen floor? With the latter, it will be a lot of extra work but I can think of a few advantage: better water pressure, less heat wasted due to cold loft ..

Hope to hear your advice. Many thanks

 

[blup]

You’ll need to leave the tank in the loft as you have an indirect cold water supply (cold taps fed by storage tank apart maybe from the kitchen). Otherwise some new pipework for fitting the combi. Your fitter will advise in detail.

Blup
.

 

[groovybug]

Hi @blup , yes currently the bathroom cold water is supplied by the water tank. However I imagine it is not difficult to reroute to main, as we have a main pipe going to the water tank nearby. However my main question is should I leave all the pipes up in the loft, or redo them under the floor.

 

[blup]

The hot water pipes will be in situ as you say the new combi goes where the old one was.

Might be some scrap copper from unused pipework in loft.

Other than that the crystal ball is not working.

blup

 

[Deleted member 267285]

Best speaking to your installer, sometimes you can have a mains fed cold distribution and gravity fed hot water distribution. Ideally your hot pipes need to match that if the outlet typically 15mm from a Combi boiler. Any unused pipework needs to be removed so as not to create a dead leg in the system (unused replenished water becomes stagnant/allows bacteria growth). Eyes on site (again your installer) would give you the best answer, you might have artex with asbestos containing material (acm).

 

[Hugh Jaleak]

Do your homework before committing to a Combi, they are not a 'One size fits all' solution, and have their limits. Going from a conventional system may leave you disappointed, there are various factors that need to be accounted for before deciding which option is best for your situation.

 

[groovybug]

@CBW I'm moving to combi so the issue was not about main fed cold/gravity fed hot. I'm asking normally when converting from traditional boiler to combi, do people move their pipeworks from the loft to under the floor? This has big implication for my renovation plan.

 

[groovybug]

Do your homework before committing to a Combi, they are not a 'One size fits all' solution, and have their limits. Going from a conventional system may leave you disappointed, there are various factors that need to be accounted for before deciding which option is best for your situation.

@Hugh Jaleak Apart from combi being able to only feed one hot tap at a time (not a problem for us really, we are only a couple), I don't see any major other disadvantage, while there is so many things that need maintaining and can go wrong with traditional system: pump, water tank, hot water cylinder etc .. plus not having instant hot water and taking up space.

 

[Alec_t]

so many things that need maintaining and can go wrong with traditional system

... but the sytem components are physically separated, generally more get-at-able, and probably a wider choice of spares. Most won't need a Gas-Safe registered engineer for maintenance.

 

[oldbuffer]

1. As Hugh Jaleak has said, make sure your incoming mains pressure and flow rates are adequate for a combi. Look for a 20 litres per minute flow and a dynamic pressure of 1.5 bar as minima. You can use a bucket to measure flow rate, but need a gauge to measure pressure. Static pressure is with everything off, the gauge connected to a mains fed outlet, and that outlet turned on. Dynamic pressure is the same as static but with another mains fed outlet running as well.
2. I'd get the installer to remove all tanks and dispose of them and any redundant pipework. There shouldn't be much requirement to re-run pipes under floors, provided the existing pipework can be terminated as necessary without creating significant deadlegs.
3. You may well find that outlets previously tank fed will need some modification, as the cold (not kitchen) and hot water pressures are likely to be much higher than at present. This applies particularly to:
3a. WC cisterns. If they are tank fed you may need new high pressure "trumpet" washer or even a new inlet valve. Not expensive.
3b. If you have a power shower (hot and cold feed, internal pump, NOT electric shower) it is likely to leak. However, given a combi you would probably replace such a shower anyway.

 

[groovybug]

1. As Hugh Jaleak has said, make sure your incoming mains pressure and flow rates are adequate for a combi. Look for a 20 litres per minute flow and a dynamic pressure of 1.5 bar as minima. You can use a bucket to measure flow rate, but need a gauge to measure pressure. Static pressure is with everything off, the gauge connected to a mains fed outlet, and that outlet turned on. Dynamic pressure is the same as static but with another mains fed outlet running as well.
2. I'd get the installer to remove all tanks and dispose of them and any redundant pipework. There shouldn't be much requirement to re-run pipes under floors, provided the existing pipework can be terminated as necessary without creating significant deadlegs.
3. You may well find that outlets previously tank fed will need some modification, as the cold (not kitchen) and hot water pressures are likely to be much higher than at present. This applies particularly to:
3a. WC cisterns. If they are tank fed you may need new high pressure "trumpet" washer or even a new inlet valve. Not expensive.
3b. If you have a power shower (hot and cold feed, internal pump, NOT electric shower) it is likely to leak. However, given a combi you would probably replace such a shower anyway.

Thank you @oldbuffer for your thoughtful reply. Yes I have checked the mains pressure, it is adequate for a combi.

My main consideration is whether to leave the pipes on the loft or re-run under floors. I know it is possible to leave them on the loft, however re-running them under floors with a combi boiler has a few advantages:


1. Loosing less heat due to shorter distance from boiler to tap/radiator
2. Better water pressure as water does not have to run up to loft then run down
3. As far as I know, most combi have pipes going out underneath, rather than above (like my Main boiler at the moment) so it's more work to get them going up on the loft first

An added consideration is I'm planning to do a loft conversion at some point as well (only bedroom and a study, not extra bathroom), so I'm not sure whether leaving the pipes on this level is better or not.

If you have any thoughts regarding this, please share with me.

Many thanks

 

[ianmcd]

where is your new combi going, is it where the old boiler is now , next to the HW cylinder ?

 

[groovybug]

where is your new combi going, is it where the old boiler is now , next to the HW cylinder ?

@ianmcd Hi Ian, I have not decided where the new combi should be yet, but I think it should be in the kitchen to minimise the distance to the taps (the bathroom is next to the kitchen).

At the moment the old boiler is in the kitchen. The HW cylinder is in a hallway closet. So flow from the boiler need to go up the loft then down to the HW cylinder then return the same way. The hot water from the cylinder also goes up to the loft before goes down to taps.

 

[ianmcd]

you just need to connect the new hot and cold pipes from the combi to the hot and cold pipes that go to the sink

 

[groovybug]

Hi @ianmcd . Yes I understand. However that's not the question I'm trying to ask. Please see my post below:

Thank you @oldbuffer for your thoughtful reply. Yes I have checked the mains pressure, it is adequate for a combi.

My main consideration is whether to leave the pipes on the loft or re-run under floors. I know it is possible to leave them on the loft, however re-running them under floors with a combi boiler has a few advantages:


1. Loosing less heat due to shorter distance from boiler to tap/radiator
2. Better water pressure as water does not have to run up to loft then run down
3. As far as I know, most combi have pipes going out underneath, rather than above (like my Main boiler at the moment) so it's more work to get them going up on the loft first

An added consideration is I'm planning to do a loft conversion at some point as well (only bedroom and a study, not extra bathroom), so I'm not sure whether leaving the pipes on this level is better or not.

If you have any thoughts regarding this, please share with me.

Many thanks