New boiler advice, standard or combi

[Elkato531]

That's an advantage for DIYers, because they can replace or fix those parts themselves.

Maybe for the likes of you and me and others who frequent sites like this but not applicable to the majority of homeowners.

someone's getting a cold shower.

In reality, if the incoming mains is up to it, the flow from the shower drops a bit for a short while and the thermostatic shower compensates to maintain the temperature. In a family situation, it is very easy to manage not having 2 showers running at the same time. I've done it. 4 bed house, three kids, 2 showers, 28KW combi. I don't remember it ever being a problem. It was certainly never the big issue that some people make out.
More likely that you get a cold shower from a cylinder because someone else has used all the hot water.

As I said in my earlier post, there are pros and cons to each type of system. For the situation that the OP describes, a combi is probably the best option.

 

[fixitflav]

For the situation that the OP describes, a combi is probably the best option

I can't agree that replacing an existing set-up with a combi is the best option. If it were a new installation there might be more of a case, but I wouldn't go for it.

 

[Fred Blogs]

Standard every time. Combis are rubbish but not as bad as heat pumps. I have a standard Worcester Boch which runs fine. I even bought a brand new spare in case the one I have packs up or the climate change/vegan nutcases decide that no-one will be allowed to sell one and makes a everyone have a heat pump.

 

[Harry Bloomfield]

Maybe for the likes of you and me and others who frequent sites like this but not applicable to the majority of homeowners.

Many owner/occupiers do attempt DIY fixes, and via this website.

 

[Elkato531]

Many owner/occupiers do attempt DIY fixes, and via this website.

Of course they do and good luck to them, but most people don't.

Combis are rubbish

Ridiculous comment and clearly not true. They may not be suited to some situations but they work very well in millions of properties up and down the country.

I can't agree that replacing an existing set-up with a combi is the best option.

Endless supply of hot water at mains pressure.
Free up loft space and airing cupboard space for other uses.
No stored hot water standing unused and cooling down
All heating/hot water components in one neat small box which can be put in a wider range of locations within the property.
No need for shower pumps which are noisy and expensive

Whenever there is a post asking this type of question, all the combi knockers stick their oar in and give a distorted view of the suitability and reliability of combis. Just trying to provide some balance.

 

[Harry Bloomfield]

Endless supply of hot water at mains pressure. However restricted, because a combi cannot produce it quickly enough.
Free up loft space and airing cupboard space for other uses. OK, and when the combi does fail, you have no other source of hot water. If a heat only fails, there can be imm heater as backup.
No stored hot water standing unused and cooling down. Hardly waste heat, for much of the year
All heating/hot water components in one neat small box which can be put in a wider range of locations within the property. One neat small, very complex box, one failure and you then wait for weeks for it to be fixed.
No need for shower pumps which are noisy and expensive In some cases, true, in others not. Even some combi's require a pump.

 

[richw]

I grew up with a traditional system, but all my own houses have had combination boilers. If it was up to me, I would never replace a traditional stored water system with a combination boiler. They are a single point of failure, and cannot supply water to more than one point at once.

The house I'm in now has a pretty poor incoming cold main, and the previous owners changed the traditional system for a large combination boiler. Not great. OK, so the water doesn't run out, but it also doesn't flow too well, and if the dishwasher, washing machine, toiler flush etc. kick-in, then your shower dribbles. Plus a long wait for water due to the terrible positioning.

 

[Elkato531]

Clearly your property was not suitable for a combi and the owners at the time were not well advised. This is unfortunate for you but should not be used as evidence that stored hot water systems are are always better.

 

[Elkato531]

Choice of hot water system usually involves compromise as there are pros and cons to consider. My advice to the OP would be to get advice and estimates from 2 or 3 local installers and to ask questions on the advantages and disadvantages of different systems in relation to their property and usage. I've installed many combis and conventional systems and have always spent time explaining the different systems to allow customers to make the best choice for them. Not all installers do this which is a shame. I've talked people out of combis when not suitable and I've convinced others to have a combi when it would make sense for them.

 

[Harry Bloomfield]

I've installed many combis and conventional systems and have always spent time explaining the different systems to allow customers to make the best choice for them.

However, your posts suggest you are extremely biased towards pushing combi boilers, despite all the potential downsides.

 

[ericmark]

I got an instant gas boiler to replace the cylinder in the old house so I could convert the room into a bedroom for my daughter, not a combi back then but two independent boilers, the problem is still had 22 mm pipe work, and the boiler takes time to heat the water, so in kitchen we got half a bowl full of cold water before the hot arrived.

Late mother got a combi because her tank was leaking, oh dear what a mess up, one she had a power shower which is illegal with a combi as it can suck water into the system, this was changed for a thermostatic shower, two problems, on Eco at taps only get hot water when a good flow, on non Eco the water at shower went from cold to hot, then cold again before finally going hot and staying hot. But at least they did swap the pipes to 15 mm.

I have solar heating the DHW in my new house, can't do that with a combi.

Old and oil boilers tend to be on/off, but modern gas boilers have a variable output, called modulating, fancy word for turning down output, the idea is as each thermostatic radiator valve (TRV) closes it at first forces more though valves still open then opens the by pass valve so hot water is returned to the boiler. The boiler senses this, and turns down the flame height (modulates) to suit, so the radiators vary in temperature until it reaches a point where the boiler can't turn down any more, then it starts a mark/space ratio to further reduce the boiler output. So the more the boiler can turn down, the longer before the mark/space ratio starts, so minimum boiler output is important, in the main combi boilers are over sized to get DHW so they are not as efficient at heating the house.

If you need the space OK go combi. But as to working as efficient as possible better with a boiler matched to CH needs rather than DHW needs.

 

[Elkato531]

However, your posts suggest you are extremely biased towards pushing combi boilers, despite all the potential downsides.

I haven't said that at all. In fact I have been careful to point out that combis are not suitable in many cases. You, and others though, seem intent on trashing the idea of a combi even when it might well be the better option. You may be basing this position on your own personal experience which is fair enough. I'm basing my views on installing, servicing and maintaining a wide range of plumbing, heating and hot water systems over many years.

 

[Harry Bloomfield]

Old and oil boilers tend to be on/off, but modern gas boilers have a variable output, called modulating, fancy word for turning down output, the idea is as each thermostatic radiator valve (TRV) closes it at first forces more though valves still open then opens the by pass valve so hot water is returned to the boiler. The boiler senses this, and turns down the flame height (modulates) to suit, so the radiators vary in temperature until it reaches a point where the boiler can't turn down any more, then it starts a mark/space ratio to further reduce the boiler output. So the more the boiler can turn down, the longer before the mark/space ratio starts, so minimum boiler output is important, in the main combi boilers are over sized to get DHW so they are not as efficient at heating the house.

If you need the space OK go combi. But as to working as efficient as possible better with a boiler matched to CH needs rather than DHW needs.

Thanks Eric another good reason to support a simple heat only boiler.

 

[Elkato531]

Most modern combis have a fairly low minimum modulation. Higher power combi boilers probably less so but I would rarely spec more than a 30kw combi.

If the OP is still following this thread, follow my advice and get some local independent installers to advise and quote. Ask them probing questions about the pros and cons of each option. Dismiss anyone who says they would always fit a combi, and anyone who says they would never fit one.

I'm not going to bang my head against this brick wall anymore.

 

[Madrab]

In a family situation, it is very easy to manage not having 2 showers running at the same time. I've done it. 4 bed house, three kids, 2 showers, 28KW combi.

I guess I'm at the other end of that spectrum then - 4 bed house 3 bathrooms - 2 are en-suite and I run an 18Kw HO with a 240L unvented and I don't have the worry of managing my 2 teenage kids, my wife and myself, if and when we want to have a shower at the same time whilst the washing machine is on and someone uses the downstairs toilet and basin. A combi wouldn't get close to suit my requirements.

I've never said it couldn't be done nor worked with (Edit) or it wouldn't be the right option for the OP - what I'm saying is why bother when there is already a system in place that can manage it all without the need to change what type of boiler is used. In all my years I've yet to find anyone with multiple bathrooms/shower, that hasn't rued the day they got rid of their stored HW and went to a combi - I have 2 clients at the moment who now want to go back to stored HW water, so they will be keeping the combi's but re-instating a cylinder.