Boiler options - Opinions welcome!

Our boiler (25 years old, same age as the house) needs replacing.

Chap from local firm who we’ve used for things before has suggested a couple of options. A direct but modern replacement, or this time a combi boiler. Both would be Vaillent boilers which I believe are decent and have 10 year guarantees.

He’s given us some advantages of combi such as instant hot water, losing the immersion and cold water tanks, bypassing the noisy pump that feeds the two showers (we no longer have a bath in the house).

Any disadvantages?

It’a a four bed house with 3 or 4 of us in it most of the time and some of what I’ve seen suggests that a combi wouldn’t usually be appropriate for a med to large house but that seems to be because of peak water usage/baths etc., which isn’t a concern. The total cost of one route including all labour is slightly higher than the other but it’s not a deal breaker. He’s suggesting combi., which is the cheaper option.

Any opinions?

Minimum hassle - replace with a modern equivalent - ?

No big system changes needed.

1 Like

I have a Vaillant combi in my 4 bed semi.
Brilliant. Efficient and quiet.
Didn’t need immersion boiler or cold water tank anymore, so gained room in my loft too!


Combis can be an issue should somebody run the hot water in the kitchen while the shower is in use.:open_mouth:
The upside of a combi is as soon as the tap/shower is off so is the gas :slightly_smiling_face:


We have just faced a similar situation after our 23 year old gas boiler reached end of life.

We too went for a Vaillant gas boiler ( 25% more efficient than our old one) and a new Grundfos water pump, both on the recommendation of our plumber. In particular he recommended the ecotec plus 424 model which he thinks is more durable/robust than the 425. We’re very happy. And have not gone combi due to no. Of bedrooms.

Re hot water tank, we chose Mixergy, which has been a revelation, hugely more efficient.

Hope this helps, BF

1 Like

One seemingly unspoken advantage of a combi is not having a hot water tank within the home during a summer heatwave. Although having said that, i wouldn’t like to be without the tank warmth in airing cupboard during the cooler months.



1- as @Guinnless says, one potential drawback of mains fed systems is someone turning on other appliances/taps etc, = some policing and sense is required.

2- the new combis are great IMHO – but if you want super-hot showers and/or a proper ‘power-shower’, they may struggle – hence why some plumbers then suggest the floor-mounted Hi-Flo ranges, which have an in-built hot tank. Either that, or you retain a hot tank arrangement.

3- can you reach an existing mains drain (not soakaway) for the condensate evacuation pipe? If not, you’ll need to run in to a buried pot with chippings.

Having had various tanks (hot and header) removed over the years, I’m comforted there’s no more potential leak points, especially when these may be located in the loft/cupboards. The downside is you can lose an airing cupboard.


p.s. I suspect you’re OK but the newer combis also need a higher-pressure gas feed than ye olde ordinary gas boilers i.e. the incoming feed in to the house is OK (noting many were re-done several years back) and also perhaps a larger diameter gas feed pipe from the meter.

1 Like

A combi only really feeds one outlet such as shower. If others run there is a significant flow reduction. I would also make sure the radiators have electronic TVRs that enable individual rooms to be heated rather than one room with the roomstat controlling whether others get heat. @Willy installed a Drayton Wiser system which is cheaper than the Vaillant equivalent.

Personally, I had an Air Source Heat Pump installed last May. I also had all the radiators upsized. They reach 36c and do the job. In colder weather I might need to increase the water temperature. I now have Solar + batteries (20kWhs) and with some overnight charging on GO the bills including EV charging are modest.

The recent cold weather has been accompanied by lots of sunshine. The solar (6300p) peaked at 27kWh. I have heated the 300m2 house using 30kWh almost entirely on solar.

Alas the capital costs are a bit higher than a replacement boiler.


1 Like

Yes cheers for the breakdown, kind of what we figured. Frankly the airing cupboard is filled with the tank, towels and old blankets, so not much airing gets done! I guess my wife could fill it with her shoes now.

The tap issue we’re aware of and is a potential drawback however I can only think someone’s possibly filling a kettle while someone else is having a shower, so not a biggy. Unless my daughter is in there…Both showers are rainfall type with an attached shower head so mains pressure is apparently OK.

I get what you’re saying about the water tanks as well.

Against my previous judgement before engineer’s visit, I am now leaning to combi. I think…

Yep, he’s going to check if existing one is OK and they can run it first. Otherwise they’ll install a fresh one, for another £300.

Like for like but modern replacement maybe the easiest, but looking into the future, any thoughts on an air source heat pump?

You’re just going to get a load of suggestions and then you’ll go with whatever your plumber guy says. Plumbers will suggest boilers that they know and make a big margin. They don’t care about how long they last and will come up with the usual rubbish that they’re only built to last 7-9 years. They can then happily fix or replace it at great cost and can sleep very happy at night.

Vaillant are good, but not quite as good as they were 25 years ago. The design of a lot of UK boilers is flawed in the first place, but as people here don’t know any different, everyone’s happy.

I looked into this about 3 years ago as my Valliant was about to go after 23 years of service. It got repaired and hasn’t had an issue since. Saying that, I know this 23 years old design is wasting 20% gas. I nearly bought an Intergas boiler. They’re built brilliantly and more importantly the design is very simple and does without key parts of the usual UK design. The only small issue is that if the plumber doesn’t fit them, he won’t go out of his way to suggest them, as he doesn’t care about you.

If mine fails, I will be getting an Intergas. I know you won’t, as that’s how forum threads go. All in the best possible taste :grinning:


Part of the issue with brands is that to be maintained as an ‘accredited installer’ (which allows the extended g’tees for punters), the installers have to maintain training records and install volumes. I had a discussion with ‘my man’ on this, as while his van has Vaillant and WB signs on it, he can be limited in what he can offer.

I know where you’re coming from, but I know where he lives. And to be fair, he’s happy with whatever option we choose. He just gave us an alternative.

The way I see it, we get some more efficiency and cupboard space with a combi. And quieter showers. The only downside is we need to fill up the kettle before someone turns the shower on. And if a combi breaks we don’t have any hot water.

Another aspect – system flushing!

To get a manu’s g’tee (hopefully ‘extended’ on both P&L), it’s generally a requirement to fit a Magna-Cleaner (or self-branded same thing) and to have a ‘system flush’ – which some cost at >£500 a go.

My man settled for a chemical wash-out (my rads/old boiler system ~ 18 y/o), rather than using the full Magna-Cleaner flow kit, which can involve tapping rads to free-up gunk in the bottom. My logic was that it would be better to simply remove, drain and wash-out the larger rads. My ‘cleaner’ continues to capture very little.

You will need a Building Reg’s certificate post the works being completed.

1 Like

Intergas is a combi. If he’s happy for any suggestions, look at the Intergas site, choose the level of cleverness you want from a boiler and tell him to fit that. Or find someone who will.

We used to be concerned about the kettle until we installed an Insinkerator filtered boiling water tap. We don’t use a kettle any more…

Best regards, BF

1 Like

I changed out my traditional boiler, located in the kitchen, for a Vaillant combi about five years back, and it’s been great, that’s in a three bedroom detached bungalow.

As long as it’s serviced annually, the warranty lasts for ten years, and a couple of parts were replaced last October at no cost.

The installer got round the issue of losing the airing cupboard by pointing out that the existing pipework could. be used for a small radiator once the cylinder had been removed, which I thought was a pretty neat idea.

It supplies plenty of oomph to my ensuite shower, at the rear of the house, with no pump needed, since the boiler is fed at mains pressure.


We went full electric with our system upgrade last year. Previously was using an LPG fed Combi with everything using mains water pressure.
We live out in the Cambridgeshire fens, where water pressure is a bit of lottery in the winter, so a system with a pressurised hot water tanks a definite benefit.
Another benefit will be that with an electric boiler, our replacement roof with Solar Panels planned for 2024 will hopefully mean that our energy costs will all but disappear.
The out lay for the Electric boiler and associated plumbing work for the Hot Tank and the long overdue replacement water main into the house was relatively high, but hopefully ultimately worth it. The removal of the Gas Tank in the garden was a day of celebration… :grin:

1 Like