Things to consider with Aga Hot Water Boilers:

AGA Rangemaster discontinued the boiler option in 2014, with modern central heating boilers doing a much better (and more efficient) job of providing domestic hot water.

Internal boilers add roughly 30-40% to the normal running costs of an Aga Cooker.

Some owners wrongly assume that the hot water inside their Aga cooker boiler is free, since the cooker is already hot. In reality, the cold water entering the cooker absorbs heat and takes it away from the internal cast iron, meaning the burner needs to work harder to restore it. Modern central heating boilers should always be the first consideration for your domestic hot water.. On average, the Aga could heat a 45 gallon cylinder twice in 24hrs. Household boilers are specifically designed for that purpose.

There is no controllability over the hot water supply.

The thermostats in traditional Aga cookers are located in the top oven. This means that the thermostat doesn't know what the boiler is doing, or is able to regulate the temperature of the water. We've had conversion customers say that their previous models used to make steam come out of the taps! Nowadays, your plumber should fit a 'blending valve' onto the cylinder or at the taps to limit water temp for current regulations. A relief valve should also be fitted to prevent pressure or excessive temperatures building up inside the cylinder.

Aga cookers were never designed to heat hot water (or heat the room!) - that's just a byproduct of their 'always on' operation. On average, the internal boilers can heat a 45 gallon cylinder twice in 24hrs. If you run out, there's no 'boost' option - you just have to wait for the cooker to catchup with demand. If you need to turn your aga cooker off in the warmer months, you'll have no hot water.

Aga Cookers cannot run radiators, only domestic hot water systems.

We've heard people looking to heat their whole home from an Aga cooker boiler, but unfortunately it's not possible. The boilers are small and don't heat sufficiently to provide hot water for radiator systems. You'd be able to run your hot tap water, and store excess inside the larger cylinder, but the maximum output would be a 135 gallon boiler (which are hard to find nowadays). The norm is a 90 gallon boiler for 2 oven models, and a smaller version for 4 oven models. The most output you would hope for would be a heat sink radiator, but you'd likely need to consider a Rayburn model instead. These have much bigger boilers inside and dedicated design for heating a radiator system.

Electric models cannot work with internal hot water boilers.

The newer controllable models of Aga Cookers tend not to have the older design of a cast iron barrel around the burner (aka, the thing that heated boilers in the past). Other electric models just aren't suitable to have a tank of water hidden inside the cooker, where leaks can go unnoticed for quite a while!

Leaks are a possibility.

There are a few versions of boilers used in the past. Original cast iron boilers for 2-oven models, are made from two pieces. The internal surface was coated in vitreous enamel, then sandwiched together with a gasket in between. These are notorious for failing over time and can cause quite a bit of internal rusting to the other cast iron components. Newer boilers were either copper, or welded steel and proved to be much more resilient. Leaks are always going to be a risk with an internal boiler, due to the connections inside the cooker body and/or the seals around the boiler. Usually, leaks aren't evident until you see puddles of water under the cooker! By that time, it's already saturated the internal insulation and requires a partial strip down to replace.

Aga cooker boilers don't last forever.

The most common reason Aga boilers fail, is due to buildup inside the pipes from the water running through them. Overtime, this slows the water flow and can cause issues, leaks or blockages. Swapping the actual boiler is a straight-forward job, but it also involves partly dismantling the cooker, removing all of the sodden insulation and renewing it.