Is it permitted to connect a combi gas boiler to the rising main

Calahonda52

I get that there may be min max pressure requirements but just wonder what are the rules, if any.

Thanks as always

C52

Sleeper12

Building regulations, Irish water regulations and local bylaws state that mains can only be connected to the cold kitchen tap & the inlet or the cold water tank in the attic. This means washing machine, dishwasher, outside tap, electric shower, combi boiler etc should not be connected to the mains water supply. In the real world just about everyone ignores these regulations. You won't go to jail if you connect to the mains & it's very unlikely it will effect the resale of the house.

Ignoring the regulations & just looking at best practice you would still connect the combi to the cold water tank in the attic with a pump between the tank & the combi. Same pump should pump the cold water from the tank. Things like thermostatic showers need equal pressure from the hot & cold feed to function correctly. Connect the combi to the mains & cold from the tank unpumped & you may need to get out of the shower and go to the combi boiler to adjust the shower temperature.

Regardless of what way you do connect the combi the plumber should inspect everything in the house. Connecting mains pressure or pumped pressure to power showers like triton as2000xt, Mira Event etc can cause the motor in the shower to blow. Pressure Reduce device would be needed in cases like that & you would be stunned at the amount of RGI Plummers that don't check these things out

Calahonda52

Thank you as always, its a client with a water tank on a felt roof and I am proposing one of the newer( al least to this gran-dad!), blue tanks with the pump and use pressure reducing kit to keep it all sensible.

Her Dad want to do the combi straight off the mains

championc

Combi's were, afaik, really designed for flats or apartments, which had no water tanks, since they had no attics, and therefore had no option / were designed to run off the rising main.

I first saw one in my brother's apartment in London about 40 years ago, and I was hooked on them, and have had them ever since, and I've never had a water tank in the attic.

So I can absolutely see where the father is coming from.

John.G

Sufficient mains water pressure is the key, if one is happy with say a showering flow of 12LPM at 40C then a 30kw combi will provide this thermally but the pressure should be checked downstairs with a pressure gauge connected to a tap while other taps are opened to give 12/15LPM, you need ~ 2.0bar dynamic. Bear in mind that there is one well known poster on here who will not install mains supplied puny electric showers in the Dublin area where the mains can't even supply the tiny 4/5 LPM required at 1.0bar at the shower, (1.5bar, downstairs).

I have 3.6bar static but only 1.0bar dynamic at a flowrate of 14.5LPM, the 22M of 50 year old 11.5mm ID of hydrodare (spelling?) doesn't help but I will get ~ 10LPM at 2.3bar, I could install a "23" kw combi based on this.

You can install one of these, but not cheap.

https://www.automatedenvironmentalsystems.co.uk/wp-content/uploads/2015/04/AES-DAB-ESYBOX-Instruction-Manual.pdf

antoinolachtnai

if you are making a big investment in your home plumbing system to improve your lifestyle and energy efficiency you might as well spend the extra hundreds of euros to make it compliant with a storage tank and pump. This cost will be for the plumber to sort out, not the homeowner

You can chance it the other way, connected directly to mains but if anything goes wrong with the outside mains you might find you have no water, or Irish Water could even ask you to fix your installation. This is not likely, certainly, but it could happen.

Plumbing the hot to the mains and the cold to a roof tank as is often done in Ireland is a completely stupid thing to do for reasons well explained above

Another stupid thing is putting in a standard size combi boiler in a five bed house with one bathroom. As sure as Christmas the homeowner will decide they want to add an extra gas-heated shower in a year or two, and now there is no obvious way to plumb this to provide two high quality showers that can run simultaneously without either adding a cylinder or replacing the boiler.

it sounds like you are giving good advice to your customer. If they want to connect direct the quotation and invoice can stare clearly that the installation was in accordance with the customer’s preferred design.

timetogo1

*Not an expert (or any way knowledgeable). Just a customer.

I got a combi boiler installed about a year ago now. They put a pump in which pumped all water to every appliance. So if the toilet flushed or somebody washed their hands the pump would come on. It was very annoying. There are 6 people in our house so the main bathroom shower can be used at any hour as people come and go. It wasn't an issue before the combi boiler as a pump was only needed for the ensuite shower. And as that shower is only used after 6AM or before 10PM it wasn't a major nuisance. The main bathroom has a shower but the pressure there was sufficient so it didn't need a pump when we had the old boiler).

I asked the plumber if the pump could be piped so it only came on for the shower as before but he showed me why it couldn't.

I saw that pumps aren't required in the UK and asked our plumber about it. He explained that the pressure over there was guaranteed, over here it's not. He said he's been to some houses where the pressure was like a weak p*ss. That's not the case in our house.

So I asked him to bypass our tank in the attic and the pump and we'd try it without the pump. He did it in such a way that we could roll back if required. The pressure in the shower is the same now as it was with the pump. So I asked him to make it permanent (tidy up the pipes and remove the water tank from the attic). It's been like that for a year now and we're happy with it.

Downsides:

If a toilet is flushed while you're in the shower the pressure in the shower is reduced for a minute (still able to shower away, just like watering can pouring on your rather than more pressurized water).

We can't use two showers at the same time. It's happened about once over the year.

If the water is cut off for any reason we don't have the buffer in the attic tank as it's gone. We only have the buffer of the one flush in each toilet. In 15 years of living here the water has been cut off about 4 times.

If we ever need the tank back in the attic and a pump installed, it's possible, so we can roll back. It's not a huge cost, but I can't see us doing it while we live here.

johnory1

Long story short , In Ireland it's regulation to install a pump fed from your water tank to supply the combi, not off the mains. It's best practice to supply both the hot and cold of the pump.

most apartment blocks are fed with boosted tank water this is where you will see combi's fed with what looks like regular mains. And anyone who installs a combi by connecting direct to mains , runs the risk of being caught with the cost of doing it properly (this happened to a plumber who installed a combi in my estate)

PeterTork

https://www.boards.ie/discussion/comment/121021096#Comment_121021096

Can you quote where it says that in the building regs please?

RetroEncabulator

Is there a particular reason why Ireland's regulations are so weird on this?

In most cases the water mains pressure is not bad. Obviously there are some exceptions to this, but in general it's not.

It just seems sometimes we've utterly bizarre plumbing by any international comparisons and the UK's historically had similar but it's at least modernising a lot more.

Sleeper12

https://www.boards.ie/discussion/comment/121488103#Comment_121488103

Current building regulations and local bylaws dating back to the early 1960s state the only the cold water tap in the kitchen and the attic tank are the only things permitted to be connected to the mains water supply. Everything else must come from the cold water tank in the attic. Washing machine, dishwasher, electric shower combi boiler etc all should come from attic tank.

Every dwelling should have a cold water tank. Even appartments are required to have their own cold water tank.

jasonlane

https://www.boards.ie/discussion/comment/121488163#Comment_121488163

Every dwelling should have a cold water tank.

Does the word "should" have the same legal meaning as "must" in these regulations? (Not being a smart arse, I'm genuinely wondering.)

Sleeper12

https://www.boards.ie/discussion/comment/121729947#Comment_121729947

Just to be clear. They don't make suggestions. Everything in the building regulations is a requirement.

Every dwelling must have a cold water tank. This is part of the building regulations, Irish water regulations and local bylaws for every country in Ireland. The local bylaws have stated this since the early 1960s. Even appartments must have a cold water tank above the hot water cylinder

championc

But surely that's the point of a Combi - there is no hot water cylinder

Sleeper12

https://www.boards.ie/discussion/comment/121730580#Comment_121730580

The question is should combi be connected to the mains water supply or cold water tank in the attic. You can remove the hot water cylinder if you want to. You will need to install another one when you get no longer get gas boilers though.

I believe this is the last year they are allowed in new builds. Another 10 years or so & it will be illegal to sell them. This is to push people into heat pumps. Problem is that heat pumps don't suit a lot of homes or lifestyles

championc

I think it's fairly safe to assume that the majority of combi's are installed in apartments, which more than likely have no attic

Sleeper12

https://www.boards.ie/discussion/comment/121731347#Comment_121731347

I think you will find the more than 99.99% of apartments don't have any gas boiler let alone a combi boiler. Apartments almost all have electric heating

The cold water tank for appartments is usually in the apartment itself & usually sitting on the hot water cylinder or actually connected to the hot water cylinder.

RetroEncabulator

I've a relative in central Dublin who's got a rising main only. It's feeding a Combi-Boiler and also an electric shower and it is FANTASTIC. She has excellent pressure and it's a really no fuss, zero complication plumbing system.

The shower flow is excellent in both of her bathrooms, one heated by the combi-boiler and the other by the electric shower.

No noisy booster pumps etc.

The tank requirement was dropped in the UK. It should really be dropped here, just depending on the state of the local supply system. If the mains pressure is good it's rather pointless, whatever about the old building regulations.

Also the concept of attic tanks is pretty gross. They inevitably get gunged up with all sorts of detritus over the years. I know I've opened the lid on one and found plenty of dead insects and all sorts of stuff. It's a rather primitive way of handling domestic water in 2024.

Inevitably people are washing their teeth with this and showering etc.

Sleeper12

https://www.boards.ie/discussion/comment/121735349#Comment_121735349

Here is the difference between the UK and Ireland. UK can have up to 10 bar of pressure. Most homes require pressure reduction valves. In parts of ireland we are lucky to get 1 bar and even if they have 1 bar at the time of testing it can drop below 3/4 bar later that evening when neighbours are using the water.

I'm in shower repair. We have to rip out most mains fed shower connected to the mains water supply because when pressure drops you don't just get bad pressure. You get stone cold water because the pressure valve can't activate & doesn't send electricity to the element.

The reason why the building regulations don't allow combi boilers and electric showers to be connected to the mains water supply isn't to spoil everyone's fun. It's because the homeowners may suffer further down the road. Cowboys that connects combi to the mains water supply won't come back to rectify their short cuts when things go wrong. Fixes can be expensive after the fact. Cheaper to install the pump at the same time as the combi boiler

RetroEncabulator

I know in my house in London you'd have been lucky to get 1 bar. The pressure was horrible.