New Gas Boiler

[Jeff Gaines]

I bought this bungalow at the end of last year, built in 1983 and the same person has lived in it the whole time. It is something of a time capsule with reasonably good quality stuff but poorly maintained. The bathroom suite is Avocado, there is Artex everywhere including the integral garage and the cupboard under the stairs. There was also a 2 mm layer of grease over everything in the kitchen, HG Degreaser and elbow grease fixed that.

I am working through cleaning/decorating/fixing and I saw the British Gas offer and wondered if it was a good deal. If I'd seen it earlier I would have asked the plumber to quote for a new boiler along with the other work he has done but I vaguely expected around £5K for a new boiler, don;t know why really except I paid about £3.5K about 15 years ago to move from an old oil fired boiler to e new condensing oil boiler with a pressurised system, perhaps gas is cheaper.

[David Wade]

Electricity hasn't gone up by the same percentage as gas...

I am on an old tariff so pay around 4p for gas and 20p for electricity so electricity is 5 x the price of gas.

On the current price cap gas is around 7p a unit electricity 27p so less than 4 times the price. So if you heat pump has an efficiency greater than 400% then it will now be cheaper to run than a gas boiler which usually has an efficiency of 95%.

This efficiency when heating is usually expressed as a simple factor, for mine its 4.5 or 450% so on the new tarrif it will be cheaper.

Dave

[SteveW]

Gas is around 7.4p while electricity is around 35p and air-sourced heat pumps can drop down to below 200% efficiency in cold weather, just when you need to use it most. Hot water also requires boosting with an immersion heater to achieve high enough temperatures.

[David Wade]

Agreed they can drop to 200% on the odd day its really cold, but typically that is only a couple of days a year. You will easily make up the loss on "normally cold days" when the efficiency can rise to 800%.

Dave

[Harry Bloomfield Esq]

Yes, but on a basic control system it will not know quite how much heat it needs to generate, so it will tend to run near flat out until demand is met. Therefore not much improvement in efficiency, apart from it being able to ramp down a bit.

The Vaillaint e-bus control system can do much better. It knows your two temperatures, knows how much heat it needs to produce so only produces exactly the amount of heat which is needed. There is none of the under-shoot/ overshoot which you get with dumb controls. The boiler also runs much quieter as a result.

[Harry Bloomfield Esq]

SteveW presented the following explanation :

The Vaillant system can do even better than that - it can decide just how hot it needs to heat the water to meet the demand for heat, rather than you setting the maximum boiler temperature.

On first install, you make a guess at an heating curve value. On subsequant runs, based on it's learning and your heat loss, it can fine tune that heating curve. It can even take into account the outdoor temperature, if you fit that sensor.

[alan_m]

Add the cost of insulating the property to a greater standard than the average UK house. The greater cost of a heat pump installation compared to a like for like gas boiler replacement (or an upgrade to a existing gas boiler). If building from new or a complete strip out renovation a ASHP maybe a consideration where underfloor heating can be installed.

I know of one person who has installed ASHP, replacing LPG, and it works well in the new (large) extension to the house that was designed/built with ASHP in mind. In the older part of the house it works less well and additional oil filled radiators have had to be used in the past winter.

There is also the temptation to spend more on electricity during the summer to use the ASHP to cool the house - not so much of a problem with cost if you invest another £10K on solar panels and a battery.

[Harry Bloomfield Esq]

David Wade presented the following explanation :

Electric prices are soaring too, maybe not quite as much as gas, but gas for heating remains the much cheaper option by far.

[Harry Bloomfield Esq]

David Wade laid this down on his screen :

Are there any heat pumps which are 400% efficient? I think not and as outdoor temperatures fall, they become less effcient/ less able to produce heat. Then add in to the cost of changing to a heat pump, that all the radiators will need to be larger, so they can work on the lower temperatures and it becomes quite an expensive option.

[Harry Bloomfield Esq]

John Rumm explained :

The 'Pure' simply means it is designed to be mounted out of sight in a cupboard or etc.. It is less pleasing on the eye.

[Harry Bloomfield Esq]

John Rumm explained on 01/06/2022 :

and disadvantage too - The boiler is much more complex, many of the problems will need a gas qualified engineer to fix them, rather than just a plumber or DIY. Potentially more wear and tear on the boiler and wasted water, because everytime a hot tap is turned on, the boiler has to fire to heat the water from cold, with water wasted until it runs hot enough. You cannot easily combine a combi with an immersion heater for back up, when the combi lets you down. Finally, filling a bath will be much slower.

[David Wade]

I think the real issue is that we expect a the same heating system to do two jobs. We see the problems in this thread where we want two temperatures from the same device. I suspect from usability heat pump type air con for heating and cooling anb a combi for hot water.

I think water driven systems, be it underfloor or normal rads are really an anachronism. The amount of heat that needs to be generated to heat the system up, and the amount stored when you switch it off means they are very unresponsive.

so under sized. Probably used existing radiators.

I think we are going to need cooling if we are to avoid deaths of elderly. To me not considering cooling is a major failing of goverment strategy.

Dave

[David Wade]

400% efficiency is a typical level down to about 4 degrees outside. at higher temps up to 800% I think we should ditch radiators and go are-2-air for room heating with perhaps a combi for water...

Dave

[Andrew]

A few hours ?. Unless it is choc-a-block full of limescale, just an hour, perhaps two at most will get it up to 60C.

You cam also take the top off the stat where there should be a temp adjustment dial and put it up a little bit to say 65C so that the heat from the top of the cylinder conducts down towards the bottom more quickly. Effective tank insulation is also a V Good idea.

[Tim+]

Eh?

Okay, if it has a built in expansion vessel that can be a bit tricky to get at but it’s hardly rocket science. It does away with a header tank and a potentially dodgy ball valve so it’s really no more complex.

Again, eh? Mostly very diyable. As long as you’re not meddling with gas connections no need to get a qualified engineer.

Ah! You’re talking about a combi, not a sealed system. A sealed system doesn’t mean a combi boiler.

Tim

[John Rumm]

You can use most boilers in a sealed system if you want - it does not imply it has to be a system boiler or combi etc. You need just to add a filling loop, pressure relief valve, and expansion vessel if using a traditional vented boiler.

I think you are conflating unrelated issues. What you describe may be true of combi boilers, but that has nothing to do with whether they have a sealed primary or not. (and you can get open vented combis as well)

Again, I was not actually talking about combi boilers. Having said that, you can combine a combi with an immersion heater if you also have a cylinder. It is not a common way of installing them, but can make sense in some applications (say when you want a cylinder for fast bath refills, bu the DHW output of the combi for mains pressure showers with no pumps, and potable hot water in a kitchen). There is nothing stopping a combi from reheating a cylinder of hot water in exactly the same way any other boiler does with appropriate controls and zoning. The fact that it can also produce hot water "instantly" is a separate function.

[Harry Bloomfield Esq]

It happens that Tim+ formulated :

Those things are all external to the boiler, so a potential DIY fix. My 'dodgy ball valve' has never been a problem in the 40 years since it was fitted, except for I replaced the metal tank and valve about three years ago.

Add to which, the whole system is under much less pressure, so less likelyhood of leaks. Even the least leaky combi's need some topping up attention, I never need to top mine up, it is automatic.

[Harry Bloomfield Esq]

John Rumm was thinking very hard :

I was working on the assumption that the OP would be looking at a more basic set up.

[John Rumm]

As was I. Keeping with a "heat only" boiler, but going for the sealed rather than vented version. Not many changes to do to the system, but it gets rid of the CH system header tank, air locks, excess corrosion, pumping over and all the other vented system woes.

[John Rumm]

That was one of the things I noticed with weather compensation - I can tell the outside temperature when I wake up based on the amount of expansion noise the heating system makes! Only on really cold days does it need to run high flow temperatures and hence the associated creaks, clanks and clicks of pipes and rads expanding!