Is a combi boiler worth the extra installation cost?

VonLuck

I currently have a standard system boiler which is about 15 years old. It regularly loses pressure and I figure that it is due for replacement. I thought that replacing it with a combi boiler would be the best option as I have a small home and don't like the idea of heating up a whole tank of water just for one shower and the rest of the hot water goes to waste.

I recently got a quote to upgrade to a combi boiler. It's estimated at around €7k all-in. I didn't realise it would be this high, but the larger costs are due to the additional pipework required to make this system work, as well as a new combi pump due to the expected lower water pressure with this system. This is not to mention painting and plastering which is not included in the cost. Some of the pipework may require a box out in my living room (as there is no service zone to run in) which is not ideal either.

The alternative is just to replace my current boiler which would cost me €3k.

I suppose the question I'm asking is whether there is a significant (€4k+ over the lifetime of the boiler) financial benefit to a combi boiler over a system boiler? My gas bill for 2023 was around €1k so if I had this new boiler for another 15 years, I would need to save at least €275 on my bill each year to make financial sense.

The other alternative is to just keep getting my current boiler serviced and not replace it until it fails entirely!

antoinolachtnai

The loss of pressure is most likely to do with the system, not the boiler. Replacing the boiler won’t necessarily fix it.

what is your hot water cylinder like?

The heat from unused hot water doesn’t really go to waste in the winter months. The heat contributes to the warmth of your home, assuming it is indoors. During the summer is a different story, but the overall point is that the loss is probably less than you think.

You could look at other things to save energy. Draft proofing, insulation, etc. it may be worth saving towards some larger item rather than doing this upgrade.

Eventually you will need a new boiler but there might be a few years in it yet and if you have cash it might be better spent elsewhere.

VonLuck

https://www.boards.ie/discussion/comment/121561568#Comment_121561568

When you say the system, do you mean solely the plumbing aspects? I've queried it multiple times when I get my boiler serviced but they don't give me any clear answer. There is the suggestion that there's a leak somewhere, but there's no evidence of that at all.

I'm not sure what you're looking for when you ask what my hot water cylinder is like? In terms of condition I assume it is fine as I've never had an issue with it with leaks. Just had to replace the stopcock a few years back.

I am in a well insulated apartment so I don't really get the benefit of the hot water cylinder heating my home. I barely turn on the radiators year round.

By the sounds of it you wouldn't recommend a combi boiler in my situation?

noodler

When I moved into my house a few years ago, I replaced the boiler with a combo.

It was old but it was also in the spare room (along with the hot tank).

So I moved it to the hall and also removed the hot tank.

About 5.5k in total (2021).

He did install a pump for the hot water downstairs and the hot/cold tap upstairs (and toilet).

It is very nosey and spits the water out at a pressure I don't like so I leave it off a lot. I was never entirely sure why it was needed - the low water pressure in the taps was sufficient for me. (I've an electric shower sadly so I get no benefit from the pump there).

Sleeper12

Heating tank of water is around €1.50 per day. You will be a long, long time trying to recover the extra for the combi at that rate.

As stated above replacing the boiling might not resolve the pressure drop issue unless it's part of the overall job

VonLuck

https://www.boards.ie/discussion/comment/121562542#Comment_121562542

Good to know. Is there any way to artificially reduce the size of the hot water tank without replacing it? Say by inserting an inflatable bladder? My thinking is that I'd only need small volumes of water at a time, primarily for showers, and it would be more efficient just to heat the volume I need.

Also, how would I figure out what's causing the pressure drop? That sounds like the first port of call!

Kaisr Sose

Agree with the economics...and there will be ongoing costs to heat water in the boiler so not saving the full €1.50 on heating full cylinder.

Have you been told the boiler is on last legs? You say it's 15yrs old but you don't use it much for heating a well insulated apartment so it should still have a lot of life in it.

Sleeper12

Heating the hot water cylinder from scratch takes about an hour using gas or oil. Putting it on for 20 or 30 minutes might be enough for you

antoinolachtnai

https://www.boards.ie/discussion/comment/121562299#Comment_121562299

So it is a modern well insulated (shiny green stuff) cylinder? Can you give us an idea when the apartment was built?

Is there an immersion on the cylinder to heat by electricity?

do you know the BER rating for the home?

How often does the heating need to be repressurised?

on the whole it sounds like you can safely be minimise your investment in all things related to gas boilers. It would be different if you had a big draughty house or a family as you can imagine.

VonLuck

https://www.boards.ie/discussion/comment/121562728#Comment_121562728

The last time I got it serviced the guy said it was still fine, although on occasion I have got a hint of the smell of gas. The guy servicing said it was fine though. I thought that it might be on the way out when the pressure constantly drops. I have to top it up every 1-2 weeks on average.

https://www.boards.ie/discussion/comment/121562767#Comment_121562767

The only problem with this is that the water doesn't get properly hot in 30 minutes. A shower wouldn't be uncomfortable, but not at the ideal temp.

https://www.boards.ie/discussion/comment/121562847#Comment_121562847

Yes, shiny green stuff! I think it was built circa 2005-2007.

There is an immersion for the cylinder, but I have not once used it as I figure it is a huge expense.

BER rating is B2. Never need to put the rads on in the hallway or kitchen/living room as it's well insulated from surrounding apartments. Bedrooms are a different story and they can get quite chilly.

As per above, the boiler needs to be repressurised every 1-2 weeks on average in order to maintain a decent temperature of tap/shower water.

antoinolachtnai

I think there must be a leak somewhere. If it was in the boiler then the service person would probably have seen it. Someone else might have a better proposal on what to do to find the leak.

If you used the top (sink) immersion with a proper timer on a smart meter deal with cheap night time electricity it would heat a smaller quantity of water to the temperature you desire. Because the element is near the top, and only the water above the element heats, it will heat a smaller quantity than the central heating coil, which is at a lower position in the cylinder. Electricitymight even then work out cheaper, especially in summertime when there is no benefit whatsoever from the lost heat. There are very cheap night time tariffs out there but they may not suit you because your overall consumption may turn out to be pretty low.

I think that it may in the future make sense to replace the gas system with an air-to-air heat pump system (not air-to-water). This would be an all-electric setup. This is not a mainstream thing to do at the moment but it may be more common in the future. That’s why I would be inclined to defer replacing your boiler to see how the market goes.

VonLuck

https://www.boards.ie/discussion/comment/121566050#Comment_121566050

Thanks for all the suggestions. Very useful.

I highly doubt there is a leak elsewhere in the system. I live in an apartment so if there was water leaking I would definitely hear about it from my downstairs neighbour!

Very difficult to gauge whether the immersion method of heating the water would be cheaper. How would you even calculate that when there are so many variables?

I did consider air-to-air, but I'm not sure how practical that is in an apartment. Might need to have an unsightly unit on my balcony, assuming it's actually permitted by the management company.

phormium

So if you seldom turn on the radiators what heats the apartment? Are you paying 1k per annum just to heat water or what else does the gas do for that money. It just seems a lot if not using radiators.

BTW I have a 32yr old gas boiler so just interested in what happens when I have to replace it!

andyd12

https://www.boards.ie/discussion/comment/121566665#Comment_121566665

At 32 yrs, a significantly reduced gas bill is what will happen

phormium

https://www.boards.ie/discussion/comment/121566724#Comment_121566724

Really though! My bill for gas is not a lot more than OP considering I have 14 radiators plus gas hob in a 2500sq ft house, heat is on twice a day on timer during cold months and provides hot water too obviously, I usually use electric shower in warm months.

I am on bulk tank LPG and interestingly the lower I get my usage the more they up the unit price! Bit of a disincentive to save gas I must say.

VonLuck

https://www.boards.ie/discussion/comment/121566665#Comment_121566665

I have two radiators, one in each bedroom which I turn on for maybe an hour a day from November to March (at a guess). The water is heated for 1.5 hours a day - 45 minutes in the morning and 45 minutes in the evening.

Is €1k a lot for that amount of usage? I don't really have anything else to gauge it against.

phormium

https://www.boards.ie/discussion/comment/121567070#Comment_121567070

Sounds astronomical to me based on my own usage.

andyd12

https://www.boards.ie/discussion/comment/121566889#Comment_121566889

What efficiency is the boiler reading on the flue gas analysis when serviced?

phormium

https://www.boards.ie/discussion/comment/121567356#Comment_121567356

Not a clue, I've never asked that obviously as I don't even know what it means but when last serviced they guy said it was working so well considering it's age that if it broke down he would consider fixing it if a fixable problem even with it's age.

It was a good boiler day one and possibly not built to be as disposable as more recent ones.

antoinolachtnai

It seems like a lot of gas alright. Can you tell us your yearly consumption of gas and electricity in kWh? €1000 a year seems like about 8000 kWh which is 21 kWh a day, which is enough to heat a lot of hot water.

If your system is losing pressure every week, there is a leak, somewhere, or something is wrong.

andyd12

https://www.boards.ie/discussion/comment/121567382#Comment_121567382

Fair enough but can't imagine it's great. Ask to see if during the next service. You can then compare vs a new boiler efficiency.

phormium

https://www.boards.ie/discussion/comment/121568041#Comment_121568041

What should it be, is there a range or number I'm looking for? Must have a look for the service sheet tomorrow out of curiosity to see if it says.

andyd12

https://www.boards.ie/discussion/comment/121568355#Comment_121568355

Should be a print out from the analyser when serviced. It will display efficiency(%)

VonLuck

https://www.boards.ie/discussion/comment/121567565#Comment_121567565

Looking at my account, my usage last year was 5500kWh which works out at around €970. Note that this is both for hot water and radiators. Is this above the norm for a two bed apartment?

People tell me that I might have a leak, but there's no indication at all. How do I find this out? I know something is wrong, but no one seems to be able to tell me what it is!

Alkers

To me a combi boiler is absolutely worth it but in your case it doesn't look like it would make sense until you're sure the existing boiler needs to be replaced in any case.

Get a few more quotes too.

Another benefit is, in the absence of a hot water tank, you gain the space where your current one is - can be very useful!

andyd12

https://www.boards.ie/discussion/comment/121570254#Comment_121570254

Its either a leak or the safety valve is faulty and allowing water to leave the system.

Can you see where the safety valve terminates? Try put a small bucket or basin underneath and see does any water collect here

VonLuck

https://www.boards.ie/discussion/comment/121570778#Comment_121570778

If it's a leak then I assume it would present itself pretty clearly with damp spots. If the pressure is dropping pretty much every week, how much water loss would we be talking about?

As for the safety valve, is that like an overflow pipe from the boiler itself? I know there's a vertical copper pipe from the bottom of the boiler which goes nowhere. Would that be it?

machiavellianme

https://www.boards.ie/discussion/comment/121570365#Comment_121570365

Apologies for hijacking, I'm in a similar situation with a 36 year old gas boiler (and gun barrel pipe work) and face a dilemma of new boiler vs new combi boiler. I've a pumped shower heated mostly through the immersion in summer, gas in winter. Apart from hot water on demand (within 30s or so) and no hot water tank, is there any other advantages of combi vs modern conventional gas boiler?

If I was to consider Solar PV later, am I better off sticking with the conventional plus hot water tank arrangement? I can't afford the ridiculous outlay to bring my 1920s house up to a B2 for any grants so trying to figure out which is better (assuming all radiators and pipework are being replaced anyway) and I won't be entertaining heat pumps as I can't get the property suitably airtight. I've zero experience of the combi and have no friends/family with it, so curious to hear feedback from others, especially those with experience of both.

Alkers

That is the advantage of a combi - instant hot water and only having to heat the exact amount of hot water you use, especially during summer.

Vs heat pump, the price per unit of gas is about 1/4 of that of a unit of electricity so even with heat pump efficiency it works out similar cost.

Re solar pv, at the moment diverting excess electricity to heat water doesn't make sense. A unit of gas to heat water costs 9c roughly and FIT for sending excess back to grid is roughly 20c per unit. So you're saving money exporting excess and using gas to heat the water. All rates are subject to change though which may change the economics of it

Kaisr Sose

https://www.boards.ie/discussion/comment/121570778#Comment_121570778

I was going to ask/suggest the same thing.

I am in an apartment too, with a Combi boiler that was loosing pressure. The pressure relief/safety valve was the cause. It's worth a check in your case

In my property it not something you can detect easily, and a service engineer may miss it as th E drop in pressure is about 0.05bar per day. The boiler outflow is plumbed into my 22mm cold water tank overflow. Over time I noticed small drips from it. A quick check of water tank confirmed it was not from there.

Your energy use seems high if you don't use the system much for heating.

andyd12

https://www.boards.ie/discussion/comment/121571236#Comment_121571236

True on the dampness particularly when topping up quite often.

Generally it is a copper pipe which is piped to outside.

Can you provide a Pic?

andyd12

https://www.boards.ie/discussion/comment/121571580#Comment_121571580

First thing to consider with a combi boiler is, how good is your mains water pressure? It will be driving everything

As a plumber, I think they are great if you have good mains pressure and your system can accommodate it.

Any domestic gas boiler in Europe would be a combi.

The idea of a cold water storage tank, hot water cylinder and a boiler all seperate and in different locations is Flintstones stuff.

Kaisr Sose

Is your boiler installed to an external wall or not on external wall?

If it's internally, the boiler safety valve may be feeding into the water tank over flow pipe (like it is in my home(. If you know where the over flow is, chexlck it to see if it's dripping. The overflow pipe may be below your balcony, or level with the bottom of your water tank, or it may even run down through the building and exit in the underground carpark! I know of one place where that's the case.

Alkers

https://www.boards.ie/discussion/comment/121572953#Comment_121572953

We have very low mains water pressure, which is overcome for the combi with a pump and expanded cold water storage tank in attic. Works fine and you'd want the pump for the shower anyway

VonLuck

https://www.boards.ie/discussion/comment/121572905#Comment_121572905

Unfortunately I'm not at home at the moment and the only photo I have on my phone is the upper section. All I know is that it is a Mynute brand boiler from about 15 years ago.

https://www.boards.ie/discussion/comment/121572985#Comment_121572985

It's an external wall. Someone suggested to me to tie a ziploc bag to that free ended pipe to see if there are any drips. I suspect that's the safety valve pipe?

VonLuck

Okay so attached are some photos of my setup. I think the overflow safety pipe is the third from the left. Any thoughts?

andyd12

https://www.boards.ie/discussion/comment/121586138#Comment_121586138

Correct that will be your pressure relief. Am I correct in saying the pipe ends here:

VonLuck

https://www.boards.ie/discussion/comment/121587029#Comment_121587029

Yup. Exactly. I've tied a plastic bag to the bottom and I will see if there's any water in it over the coming days.

If there's nothing there is the only other possibility a leak in a pipe somewhere?

andyd12

https://www.boards.ie/discussion/comment/121588141#Comment_121588141

See how you get on.

It could be leaking in the heating within the floor. Also it could be leaking in the coil of your cylinder into your hot water.

Hard to diagnose without being there

Kaisr Sose

https://www.boards.ie/discussion/comment/121588141#Comment_121588141

That would be correct. Odd set up! Have you a drain under that pipe?

VonLuck

https://www.boards.ie/discussion/comment/121589249#Comment_121589249

I imagine that a leak from the pipes in the floor would present itself very quickly, either seeing it myself or else complaints from the neighbour below

How would you find out if it's the latter, a leaking in the coil of the cylinder?

https://www.boards.ie/discussion/comment/121589304#Comment_121589304

Is it? What normally happens? The boiler is on a balcony so if it ever overflows it would just go to my below deck balcony drainage I guess.

Sleeper12

https://www.boards.ie/discussion/comment/121572953#Comment_121572953

Combi boiler should never come from the mains. It's against the building regulations and local bylaws. Combi should be connected to the cold water tank in the attic. Hot and cold feed from the tank should be pumped. Thermostatic mixers require equal pressure. They can't function correctly with mains pressure on the hot & gravity on the cold. This also voids most warranty on mixers or showers

Yellow_Fern

if you replace the boiler, get a good one that does hot water priority and set it up with weather compensation, like the Ideal Vogue. Makes a big difference to running costs.