Regular boiler switch to combi - initial advice

[elsmandino]

Hi there.

I have an old fashioned boiler in my 3-bedroom bungalow, which I am thinking of switching out for a combi - the current boiler is from the 90s!

The boiler is on an outside wall in the kitchen and the hot water tank is an airing cupboard in the main bedroom (which is next to an outside wall).

Just a few initial questions to get the ball rolling:

1. Should I try and get this work done now or until after winter?

2. Will I have to upgrade my current pipework (and even radiators) to work with a combi?

3. Where do people tend to put combis, when they do a straight swap - i.e. is it less work to put the combi where the current boiler is or where the water tank is, or does it literally make no real difference?

TIA

 

[vulcancontinental]

The combi will be your source of hot water so put it near the tap you use most or partway between kitchen and bath. As you'll need a new gas run probably the meter position may have a bearing on things. If your rads get hot now why wouldn't they with a new combi probably with a more powerful and probably too powerful pump. Get the system flushed properly. There's more of course but that's a starter. As for when, most manufacturers have had a big price increase this year if not two. If you have a brand in mind that might be important. Some are holding this years prices till January.

 

[elsmandino]

Thanks so much for that - really helpful.

I might be getting things very mixed up, but I was under the impression (having watched a few youtube videos) that the pipework for a combi boiler has to be wider. Something to do with the fact that temperatures have to run cooler, now, and that means that a higher flow rate is needed to get the same heat from a radiator.

 

[ericmark]

With a hot water tank you can fit an immersion heater taking power from your solar panels, once converted to a combi you loose this option.

Also some combi's cheat, many oil combi boilers still have a hot water tank, it is just smaller and hidden inside the boiler, so really all you are doing is fitting a smaller hot water tank. For gas the boilers can often modulate, so you can have direct hot water, no tank, but often a tank is fitted so you get hot water fast, and you can stop using the tank by using the Eco setting.

Using a shower with a combi where Eco setting not selected can mean starts cold goes hot then cold then hot again as tank runs out before the boiler has got up to heat.

Also most homes only need around 15 kW of central heating, so a boiler (gas) can modulate from 4 to 15 kW with ease, giving central heating with no hysteresis, but with a combi that would take an age to fill a bath, so more likely a 28 kW boiler is fitted, which will likely only modulate down to 8 kW so it has to cycle off/on, so more hysteresis in room temperatures.

My last house added a instant heat water boiler in the garage so the room where the cylinder was could be enlarged and turned into a bedroom, it was a good move, but after some 25 years one of the boilers started to leak, so swapped both for a single combi, seemed to make sense to combine them. However every lock shield valve started to leak, as new boiler did not use header tank. So a little more work than first intended.

I expected to see the gas bill drop, since now using a condensing boiler, but could see no change, however on moving to this house with an oil boiler, much larger house, but heating bill dropped.

As to why heating bill did not drop don't know, son had moved into the house, now with new front and rear doors, so less drafts, but no longer my problem, he has bought the house.

 

[Madrab]

The first thing I would check is the gas supply. With a large number of lower input conventional boilers, a 15mm gas supply would be enough, I can just about guarantee that the combi will require a 22mm supply at least.

Why do you want to change to a combi, is it just the space return when removing the cylinder? How many bathrooms, hot water outlets would typically be used at the same time?

Any gas central heating can use 22mm > 15mm and/or 10mm radiator supply pipework. The ideal would be a 22mm backbone with branches of 15mm to each radiator to minimise heat up times, though you may find you already have that. Ideally new condensing boiler run with a return temp of ~50deg, that's to ensure that it condenses properly, so it's at it's most efficient. The system pipework size doesn't really affect that requirement though.

 

[vulcancontinental]

I tied to come up with some useful tips but madrab pointed out the big one I missed: why?

Always, always, always; what do expect to achieve or change or improve?

 

[elsmandino]

Thanks.

One main factor for this is that we are thinking of moving in the not too distant future (certainly within 2 years). Our current boiler is so old that it would almost certainly be a turn off of any potential buyers.

The research I have been doing, so far, suggests that combis might actually give us a net increase on the house value, when you take into account the efficiency and space that they free up - in particular, we would gain a huge closet where the tank was in the master bedroom and the loft could then be a potential conversion space for a buyer in the future.

On a personal level, I think a combi might be a good fit for my family as well. My wife always seems to be complaining that there is never enough hot water - for some reason we seem to use a lot of hot water all at the same time, which I still cannot quite get to the bottom of.

Combis do seem to be a bit marmite, from what I have read, though.

 

[pcaouolte]

A family home with high hot water demand is a good fit for stored hot water. Combi boilers are better suited to smaller properties with lower hot water demand. It sounds like you might actually benefit from a larger hot water tank.

 

[Harry Bloomfield]

I might be getting things very mixed up, but I was under the impression (having watched a few youtube videos) that the pipework for a combi boiler has to be wider. Something to do with the fact that temperatures have to run cooler, now, and that means that a higher flow rate is needed to get the same heat from a radiator.

Modern boilers do work more efficiently at lower water return temperatures, but that will not affect the size of your pipes, assuming they are 14 and 22mm pipe runs. Larger/higher output radiators will help achieve lower temperatures, but....

If your present radiator designs were designed before you did improved insulation, better loft insulation, cavity wall insulation, double glazing etc., they may be satisfactory as they are.

Are the pipes to your radiators perhaps 10mm OD?

 

[Harry Bloomfield]

On a personal level, I think a combi might be a good fit for my family as well. My wife always seems to be complaining that there is never enough hot water - for some reason we seem to use a lot of hot water all at the same time, which I still cannot quite get to the bottom of.

Combis do seem to be a bit marmite, from what I have read, though.

In my opinion, conversion to combis are over sold and maybe not always the best solution to every problem. You should be assessing why you run out of hot water so quickly, as a first step. What size is your hot water cylinder and what temperature is the thermostat set to?

For reference, I can take a very hot bath and before I get out 20 minutes later, my boiler has replenished the temperature in the cylinder back and it is ready for a second bath should it be needed. Two concurrent hot baths would be a problem, but we only have one.

Also keep in mind, that the gas supply pipe from meter to boiler will almost certainly need to be replaced with a larger pipe for a combi. Combi boiler needs to be higher Kw output, hence the larger pipe, the extra Kw output makes them less efficient for space heating, because they need to be sized for instant water heating.

 

[JohnD]

I know nothing about the price of boilers, but with inflation running around 10%, if you have the cash available, it will diminish in value over time.

 

[elsmandino]

If your present radiator designs were designed before you did improved insulation, better loft insulation, cavity wall insulation, double glazing etc., they may be satisfactory as they are.

Are the pipes to your radiators perhaps 10mm OD?

This is very good point - I know that the radiators were put in before double glazing was added by the previous owner.

Also, my loft is only partially insulated - i.e. only 100mm in parts, if at all. I am, in fact, starting to put in 270mm before Christmas. As you say, with all that extra insulation in place, I might find that the radiators are more than adequate.

I did a bit of measuring and the pipe that runs along the corridor floor is 25mm. The pipes that run up and into the radiators are 17mm.

Just out of interest, I checked the boiler and it is called a Barlo Balmoral 45F.

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Not quite as old as I first thought but, by no means, a spring chicken.

One of things that is really complicating things is the fact that I am thinking of selling the property soon. I read, from a few guides, that adding a modern combi boiler to a property can add £8,000.00 to its price.

However, I am not sure that this is the case, now.

In particular - all the bungalows down my road have been substantially increased in size and I no doubt think that any potential buyer will be thinking of doing the same and it seems that combi boilers aren't really best designed for bigger properties like that. That being the case, they might then be a bit irritated to find that I have gotten rid of all the kit (water tank, loft tank, pipework) that they then want.

Conversely, the purchaser may want to stick with the property at its current size and decide that a combi would be a good idea - if I have a new upgraded boiler, they might then try to argue that the property is missing a combi and I have then wasted the money on an upgrade.

Do you think I should just sell the heating system as it is? The buyer therefore gets the opportunity to make the ultimate decision on how what they do with it?

 

[pcaouolte]

One of things that is really complicating things is the fact that I am thinking of selling the property soon. I read, from a few guides, that adding a modern combi boiler to a property can add £8,000.00 to its price.

Do you think I should just sell the heating system as it is? The buyer therefore gets the opportunity to make the ultimate decision on how what they do with it?

I don't understand why fitting a combi boiler would add more to the price of the house than the cost of getting one fitted by the buyer. If I was buying a family home with a combi boiler I would want to reduce the price to cover the cost of getting a proper boiler with a hot water tank installed.

Yes, sell it as it is.

 

[Harry Bloomfield]

I did a bit of measuring and the pipe that runs along the corridor floor is 25mm. The pipes that run up and into the radiators are 17mm.

Just out of interest, I checked the boiler and it is called a Barlo Balmoral 45F.

Once you deal with your insulation, likely your radiators should IMHO fine.

One of things that is really complicating things is the fact that I am thinking of selling the property soon. I read, from a few guides, that adding a modern combi boiler to a property can add £8,000.00 to its price.

However, I am not sure that this is the case, now.

I'm not sure that was ever the case. A conventional system as you have, would cost much more to install from scratch, than a combi. A combi is well worth changing to in a small flat, or house which is in use irregularly, or which is desperately cramped for space. One other thing worth checking is the two header tanks, they should now be plastic versions to avoid them rotting out and leaking.

I have twice had heating engineers here trying to convince me to swap to a combi, and no way would I have one. I have in the past had experience of waiting for baths to fill and no hot water when they fail. If a conventional heat only boiler fails, your can just switch on the immersion heater until fixed. Lower pressure in the radiators, means less chance of leaks too, and none of the sometimes regular topping up if there is a slight loss. A heat only is also much less complex, cheaper to install and repair, if something goes wrong and less to go wrong. More of what can go wrong is a simple fix external to the boiler anyway.

 

[elsmandino]

Great - thanks, guys.

I perhaps should take these "how to add value to your home" guides with a bit of a pinch of salt. I couldn't work it out, either - assumed that it was something to do with the purchaser not having to deal with the inconvenience of installation.

Thanks, also, for the tip on the header tanks - can indeed confirm that they are plastic.

Just need to make sure that I put some extra lagging on that and the pipes as my cold loft is about to become a bit colder with all that extra insulation I will be whacking up there, shortly.