Advice on replacing my CH system

[Harry Bloomfield]

Thanks for all your advice, I haven’t quite worked out yet if it’s all made me wiser or more confused, but I am certainly grateful for it!

A further question, if I may: after reading some replies would I be correct in thinking that with a Combi the hot water flow will be slower? That would be a problem as we already have a fairly slow flow and presumably our shower (mixer tap on the bath) would become unusable.

The hot pressure might well be higher than via an open vented system, but that depends on how good your cold supply is - both pressure and the flow. A normal combi has to heat the water instantly, so it needs to have a much higher Kw rating than an heat only boiler. The hot water flow via the boiler, might need to be reduced, to achieve the desired output temperature, whereas you can draw hot water from a hot cylinder at whatever speed the system will allow.

I have an open vented system and visitors who have a combi at home, are often surprised at just how quickly the water runs hot and how quickly a bath can be filled.

 

[Mottie]

Doesn’t the temperature of the hot water also depend on the temperature of the incoming mains? When we had a combi in our old house, we had to turn the flow to the boiler right down in winter to get a decent temperature of hot water out. Took bloody ages to fill a bath.

 

[Harry Bloomfield]

Doesn’t the temperature of the hot water also depend on the temperature of the incoming mains? When we had a combi in our old house, we had to turn the flow to the boiler right down in winter to get a decent temperature of hot water out. Took bloody ages to fill a bath.

I have no experience of modern ones, but I think they self modulate the flow of water, if the flow is too much to achieve the desired output temperature.

 

[sxturbo]

I would not advise a combi unless the house is small with only 1 bathroom, and there is only 2 occupants in the house.

A hot water tank is much more beneficial to the ease of living, for example you can have a shower at the same time as someone washes their hands.

The boiler takes less abuse when it heats a hot water tank, with a combi everytime the hot water tap is switched on it also switches on. Probably not to it's detriment but it's still extra work.

With a combi if the boiler breaks you have no hot water or heating, at least with a water tank you still get hot water if you have an immersion.

All the combis I have used none have had decent hot water and the flow has been slow.

I grew up in a house that my dad fitted a combi to, and then my first house was a combi, and my current house is a system and its much more comfortable.

Personally I would recommend a sealed system heat only boiler.

Boilers these days are quite small and many are designed to fit into a high level kitchen cupboard.

Personally I wouldn't go for an unvented cylinder, you have to have it serviced by a G3 approved agent every year, there are various safety devices which can and do go wrong and it just adds complexity which isn't needed. If you want better hot water flow fit a pump.

Boilers to go for

Intergas
Baxi
Atag
Vaillant (not vaillant combi)
Veissman
Vokera

I wouldn't advise Worcester Bosch.

 

[Harry Bloomfield]

I would not advise a combi unless the house is small with only 1 bathroom, and there is only 2 occupants in the house.

A hot water tank is much more beneficial to the ease of living, for example you can have a shower at the same time as someone washes their hands.

To that, I would add, combi boiler are a cheaper, less involved option than an open vented system at the new install stage. Where there is already an open vented system, it is worth while to keep it as an open vented.

 

[denso13]

Where there is already an open vented system, it is worth while to keep it as an open vented.

Sometimes. No two jobs are the same and it is better to do a proper on site survey and advise what system is best.

 

[bernardgreen]

Boilers to go for

Intergas
Baxi
Atag
Vaillant (not vaillant combi)
Veissman
Vokera

There are several other lesser known brands of very good quality and reliable boilers.

 

[sxturbo]

To that, I would add, combi boiler are a cheaper, less involved option than an open vented system at the new install stage.

Very much agreed

 

[sxturbo]

There are several other lesser known brands of very good quality and reliable boilers.

Please add them

 

[bernardgreen]

Please add them

I have a Johnson and Starley Reno 16 So far 9 years with only one minor problem.

 

[pyounger]

Not necessarily, it depends how slow it is at the moment. The hot and cold will both be at mains pressure so showers generally tend to be better (depending on water pressure/flow of course).

Some gravity hot water flows are very poor and are helped by installing a combi.

that’s good our mains flow is very good, our hot water (gravity fed) is not, so maybe I’ll benefit from a Combi

 

[M4ni]

that’s good our mains flow is very good, our hot water (gravity fed) is not, so maybe I’ll benefit from a Combi

We changed from a gravity system to an Intergas combi with a nest thermostat, the DHW at almost mains pressure was a real bonus.
Intergas support chap tweaked a few things for us after it was installed heating side is closer to 12kw now and the DHW reduced as default 55c is crazy hot.

Also the Intergas combis seem suited to older CH piping as you can set them up @ 1.0 bar and work just fine. If you need to add a tank later you can easily set them up as a system boiler too.