combi or condensing boiler

[brums evil twin]

we have a condensing boiler at present and its been with a us a good chunk of time. Typical the day I fly off for work it goes and dies = pissed of wife as she has no hot water of heating.

Anyway, engineer been out and its internally bksed and need a new one.

So our choices replacement of the same / similar condensing OR change to a combi and get away from the water tanks in the loft.

BUT with a combi I will need to replace the shower too - I have a digital low pressure Mira that will have to change to a high pressure one on top.

The difference seems to be £3k for the condensing and £4k PLUS £700 for the shower for the combi.

Are the saving on running worth it? not sure which way to jump

thanks

[OutInTheShed]

I would not pay extra to change to a combi boiler, unless there were overpowering reasons like a loft conversion needing to lose the header tank.

Combis have their downsides, including annoying delay while they fire up and heat the water.
They do have pro's as well as cons, but I'm tired of mine.
But not to the point of paying real money to change to any other system.

A HW cylinder allows using solar power to do your HW in summer at some point in the future.

I would do some research about control systems, I'm out of date, but for optimum efficiency you want something that allows low flow temp for your CH, but higher flow temp for your HW cylinder. To be fair to combi's that is easy with them.

You could also make up your own mind about heat pumps, but that is less likely to be a quick fix.

There are a few long threads on here full of advice and opinions,

[WhiskyDisco]

We use a large system boiler, which I think is another term for a condensing boiler. We use it for heating, and for heating a massive megaflo. Although I sometimes wonder about the benefit of heating all that water to store it things seem to worm fine for us. 3* showers running concurrently.

[Little Lofty]

All new combi's are condensing. It’s a long time since I had a hot water tank but the last time I changed to a combi I did use less gas, I think at the time it was £10 ish per month, that could be £30/40 now with the price of gas. It could take the life of the boiler to get your money back, it will all depend on your usage. I changed as the boiler was knackered, and getting a combi put it the garage freed up space in the kitchen and gave be back a big cupboard where the tanks were, your swap is less advantageous.

[brums evil twin]

Thanks guys

Having a second quote today and a second opinion

But seems now, £2600 to replace the condensing and £5200 for the combo including new shower. I am feeling it’s not worth the extra.

[MattyD803]

As mentioned above, be careful of your terminology to avoid confusion when getting quotes. ALL domestic boilers these days are condensing, so you can drop that descriptor in any case. There are 3 main types of boiler:

1) Combi (Produces hot water and heating, pressurised system, no external tanks used)

2) System (Pumps and Valves are integral, used on a pressurised system, separate hot water cylinder)

3) Conventional or Heat Only (Pumps and Valves are external, separate hot water cylinder, typically installed where there is a cold water tank)

The type of installation you have in your house at present will depict whether it is a System or Conventional boiler you require as a 'like for like' replacement...but I am assuming conventional, as you mention a 'low pressure' shower...?

[cliffords]

MattyD803 said:

As mentioned above, be careful of your terminology to avoid confusion when getting quotes. ALL domestic boilers these days are condensing, so you can drop that descriptor in any case. There are 3 main types of boiler:

1) Combi (Produces hot water and heating, pressurised system, no external tanks used)

2) System (Pumps and Valves are integral, used on a pressurised system, separate hot water cylinder)

3) Conventional or Heat Only (Pumps and Valves are external, separate hot water cylinder, typically installed where there is a cold water tank)

The type of installation you have in your house at present will depict whether it is a System or Conventional boiler you require as a 'like for like' replacement...but I am assuming conventional, as you mention a 'low pressure' shower...?

Good post well set out.

[brums evil twin]

Hmmmm okay and thanks

I admit I know nothing about these and thanks for the descriptions.
We have a separate cold and hot water tanks in the loft and a boiler that heats both the hot water tank and the heating.

It definitely condenses as it has an external pipe that has frozen up in the winter before.

Trying to sort all this while I am working in Singapore and not being able to be there when the engineers are looking at it is tough.

Thanks for the input. I a, just going on what they have told my wife.

[brums evil twin]

Just thinking again, ours is definitely pressurised so a think a ‘system’ set up is what we are looking at replacing

[Chrisgr31]

We have a combi boiler and I hate it with a passion. The current one replaced the combi installed by the previous house owner.

Some of the issues are down to the installation I suspect. It takes an age for hot water to reach the kitchen and downstairs toilet taps. I suspect this is because the hot water tank was upstairs so the water goes from the boiler upstairs to join the original plumbing and back down.

Flush a toilet in the house and there instantly is not enough water to power the shower.

I’d be careful of changing a system that currently works. The heat loss from a modern hot water tank I suspect is little.

[White-Noise]

Chrisgr31 said:

We have a combi boiler and I hate it with a passion. The current one replaced the combi installed by the previous house owner.

Some of the issues are down to the installation I suspect. It takes an age for hot water to reach the kitchen and downstairs toilet taps. I suspect this is because the hot water tank was upstairs so the water goes from the boiler upstairs to join the original plumbing and back down.

Flush a toilet in the house and there instantly is not enough water to power the shower.

I d be careful of changing a system that currently works. The heat loss from a modern hot water tank I suspect is little.

I have this issue with the hot water taking so long after I switched to a combi from a system. I don't like it.

I had to do it to gain the space I needed in the loft but it definitely would make me think twice.

In your situation given the price difference, plus you're away, I would be leaning to the system unless you need to lose the tanks etc specifically.

Note I'm no expert just my thoughts

[Chrisgr31]

We have a combi boiler and I hate it with a passion. The current one replaced the combi installed by the previous house owner.

Some of the issues are down to the installation I suspect. It takes an age for hot water to reach the kitchen and downstairs toilet taps. I suspect this is because the hot water tank was upstairs so the water goes from the boiler upstairs to join the original plumbing and back down.

Flush a toilet in the house and there instantly is not enough water to power the shower.

I’d be careful of changing a system that currently works. The heat loss from a modern hot water tank I suspect is little.

[gmaz]

Is your house suitable for an air-source heat pump. You can get a grant of £7500 towards the cost, so replacing my boiler and adding an unvented cylinder cost me about £3800 for £11,300 worth of kit. Check the Octopus site if interested.

https://octopus.energy/heat-pump-explore/

Edited by gmaz on Wednesday 22 October 17:31

[Russet Grange]

Another big vote for any system that uses a big tank for hot water. Why? Because you can whack an immersion heater in it, and heat an entire tank of hot water on Octopus Go overnight rate of 8.5p/kwh. That's about 60p/day with zero wear and tear on the boiler as an added bonus.

If you want a bath later in the day you'll need to run the boiler, but even then you've got your tank still fairly warm as a baseline for heating up from.

[Gaumon]

As already mentioned, combi boilers suffer from annoying delays - especially when the boiler is fairly remote from the main hot tap (installed in a garage, for example).

Even more annoying if you start and stop the hot tap a few times:

• open tap - cold water initially flows, which gradually heats up to full temperature
• close tap for a minute then open again - lukewarm water flows, followed by a burst of superheated water from the heat exchanger. Then more coldish water which gradually heats up again!!

'System boilers' - with internal pump, valves, and (usually) expansion vessel - are easier to install,, but are often more difficult to repair. A simple 'heat only' boiler with these components fitted externally is often a better bet unless you're really pushed for installation space.

[MattyD803]

Whilst combi’s ‘can’ be slower to fire up and produce hot water, don’t be under any impression that water from a hot water cylinder comes through instantly. The only way you could gaurentee that would be with a pumped return circuit, which has its own draw backs.

Nonetheless, whether it’s a combi or tank, delivery delay is all dependant on pipe sizing, locations of kit/outlets and available pressure/flow. Sounds like those complaining on this forum may have a poorly configured system.

A properly designed and spec’d combi can be very effective & efficient. We have a 4 bed / 2 bath property with a Vaillant combi and we’d never chose to go back to a system with a storage cylinder. In a busy house with 2 teenagers, many baths, lots of car washing etc, unlimited hot water, at any time without any ‘boosting’ etc is a non-negotiable.

[Gtom]

Another negative with a combi boiler is that while it’s making hot water, it’s not heating the radiators.

Get a family of 4 all using the shower in the morning and you will be losing a fair amount of time with the radiators to getting warm.

[ashenfie]

Many good points here. I have a combi boiler but would consider a system boiler in the event I was going to get solar in the future. You could heat the water in the tank during the day and store it over night. In terms of heat pump while currently you can get a grant that covers 60% or the cost of installation. in a few years time these grants are likely to be gone, leaving the a very niche technology only the rich could afford.

[MattyD803]

Gtom said:

Another negative with a combi boiler is that while it s making hot water, it s not heating the radiators.

Get a family of 4 all using the shower in the morning and you will be losing a fair amount of time with the radiators to getting warm.

This is not incorrect, but the impact in reality is negligible, when you consider thermal mass at play. By which I mean, the heating was likely running before the showers commenced, meaning you've already started your way up the heating curve and the circulatory fluid will not turn cold immediately, but will still be pumped. Hence you've got a decent 'grace' period and further climb or plateau of internal temps, before you'd start noticing a significant drop off in heating output, but more importantly, feeling the house cooling.

The only way I could that being as issue would be if all 4 people go into the shower, one another another for 15 mins each, at exactly the point in time you've asked the heating to come on, on a particularly cold winter day, in a house with poor insulation etc. What with predictive heating / heat up timers on most modern systems, I don't imagine this ever really being an issue. Certainly never has been for us (family of 4, all showering in the morning).

However, as mentioned above, what with ASHP and Solar integration, I suspect at our next heating system renewal, we will need to look to have to incorporate a hot water cylinder....but it certainly won't be being driven by improved operational performance .

[budgie smuggler]

Chrisgr31 said:

We have a combi boiler and I hate it with a passion. The current one replaced the combi installed by the previous house owner.

Some of the issues are down to the installation I suspect. It takes an age for hot water to reach the kitchen and downstairs toilet taps. I suspect this is because the hot water tank was upstairs so the water goes from the boiler upstairs to join the original plumbing and back down.

Flush a toilet in the house and there instantly is not enough water to power the shower.

I d be careful of changing a system that currently works. The heat loss from a modern hot water tank I suspect is little.

Some combis have a hot water pre-heat function, it's worth checking if yours does, as it makes quite a difference. Some boilers default to their 'eco' mode which disables it.