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Gledhill Boilermate explained


 Thermal Stores

Gledhill Boilermate explained

Understanding Boilermate and your options for replacement

Index Page > GLEDHILL PRODUCTS > Boilermate Explained


Know your Boilermate


Gledhill Boilermate

The product known as 'Boilermate' has been around for a long time. It has however evolved during this time and if you are replacing an elderly unit (or for that matter planning to incorporate one in a new installation) you should be aware of fundamental differences between old and new models.

What is a Boilermate?

A Boilermate is a Thermal Storage unit. But the full answer to this rather depends on the age of the unit as the function and appearance has somewhat altered over the years.

Pictured right you will see a Boilermate A Class OV - very different in appearance to a Boilermate II for example, or the newer Boilermate BP shown below.

A thermal store, as the name suggests, is something that stores thermal energy. Thermal stores, as they are generically known, are available from different manufacturers and typically store their energy in a mass of water contained within the unit which is open vented - this is to say the water stored is at atmospheric pressure, not sealed, pressurised or 'unvented'. Rather like a massive bucket. Gledhill (the manufacturer of Boilermate) took the principle of an open vented thermal store (a concept favoured for it's safety when compared to unvented systems) and incorporated several functions into their unit and gave it a snazzy name.

As mentioned, the Boilermate unit has changed both in appearance and function due to product development (and other factors) over the years. The earlier models looked like a cylinder with various pipework, whereas newer versions resembled a rather unassuming office cabinet with concealed pipework. Interestingly, the most recent version (2020) is cylindrical once again.

Gledhill Boilermate A Class with front cover removed exposing internals

What function does a Thermal Store perform?

The core function of a thermal store is to collect and store energy. Hence, a Boilermate is an energy store. But, the Boilermate (depending on model) utilises the stored energy to perform other domestic services. The most desirable function of a thermal store (and therefore a Boilermate) is to provide provide mains pressure hot water whilst remaining safely open vented. A contradiction you might think (mains pressure hot water from an open vented store?) but this is the somewhat clever part - heat contained within the store is simply imparted to mains pressure cold water passing through the unit. The method by which this operation is achieved marks the difference between products offered by manufacturers and indeed the different models within the Boilermate range.


What function does a Boilermate provide

To answer this fully rather depends on the version of Boilermate.

Going back, the 2000 and A Class models were an 'all-in-one' hot water and central heating management system contained conveniently and neatly in an unobtrusive beige cabinet. Considered ideal for rapid and almost foolproof installation, the unit could be wheeled in and with a few simple connections central heating and mains pressure hot water were achieved.

Designed to work in conjunction with a boiler (hence the name 'Boilermate') the product soon became popular with major housing developers not only for it's performance but also for it's ease of installation. Delightfully simple for the plumber, a full water management system in a single product - and no fiddly items of valuable stock for the developer to leave on site and keep an eye on!


Evolution of Boilermate

Over many years the Boilermate has evolved from a cylindrical thermal store (pre-2000) with a host of visible pipes and external components into a neat cabinet containing everything the unit needed to perform it's function concealed behind a removable front panel.

Mains pressure hot water, a fully open vented store (a great safety feature), central heating control, boiler control, all the pumps and gadgets needed to manage household requirements were incorporated into the Boilermate.

As the product continued to develop (Boilermate 2000 and later) the unit saw the introduction of an optional 9kW electric boiler that could be used in emergencies if the main boiler were to breakdown. This feature became a standard fitment on the Boilermate 'A Class'. Little by little the unit became more and more 'clever'.


How do you get mains pressure hot water from an open vented thermal store?

The principle is simple, although achieving it is somewhat more complex. What appears to be a contradictory scenario is achieved through heat exchange.

Heat exchangers are utilised to take pre-heated water from the thermal store (which is open vented) and impart the energy into the mains pressure water passing through the unit via a heat exchanger. It's as simple as that. All of the dangers (risks of explosion) associated with unvented cylinders simply disappear because an open vented store cannot become pressurised. So you get all the benefits of mains pressure hot water with none of the risks.


Reliability of the Boilermate

The Boilermate continues to be a good idea. To exploit elements that safely deliver mains pressure hot water without any of the dangers must be a good thing, but Boilermate hit a bit of a problem - it became complex.

Boilermate had developed into an entity that required an electronic brain. Although heat exchange technology is simple to achieve, stabilising output temperature opened up a new can of worms. In order to utilise a plate heat exchanger with a high flow potential AND achieve a stable output temperature the speed at which water from the store was pushed through the heat exchanger had to be regulated, taking into account things like the speed of flow and temperature of the incoming mains water. Then there was the temperature of the store water which would be constantly changing. A target hot water output temperature of 55 degrees C was achieved by modulating the pump circulating the store water through the heat exchanger accordingly.

Control required a microprocessor which of course gave rise to the need for electronics and circuit boards. Electronics took over the control of all system functions. With complexity can come an increase of things to go wrong. Whilst generally reliable, if something did go wrong there were precious few plumbers who felt able to understand let alone fix such a unit. You were likely to get injured in the rush for the door as the tradesperson legged it!

Plumbers were alarmed when they saw electronics and circuit boards and would often jump to the wrong diagnosis if fixing a problem - blaming a circuit board (the most expensive bit) for example rather than a simple temperature sensor (the cheapest bit).

Suffice to say, finding a willing plumber was difficult, but finding one who could understand the Boilermate could prove very tricky.


Getting a Boilermate fixed

In reality the function and principle of Boilermate is not all that complicated, it just needs a willing and open mind. Principles of thermal storage are in themselves fairly easy to grasp, but many plumbers either can't be bothered or become petrified at the thought of learning something new. For this reason owners of Boilermates around the country are happy as can be while they work, it's when they go wrong it becomes apparent that help is in short supply.

Models of Boilermate up to and including the 'Boilermate A Class' were good at what they were designed to do so long as they didn't go wrong. It can be difficult to find a person who will understand and tackle a repair. Spares can be a little pricey.


The new generation of Boilermate

Towards the end of the 2000 decade the Water Storage division of Gledhill that manufactured the Boilermate went into liquidation. It's reliance on the 'new build' housing market proved to be the downfall. Boilermate as we knew it ceased to be.

However.... Gledhill is made up of several divisions, so manufacture of the Boilermate range (along with other products) transferred to the Building Products division. From then Boilermate would carry a 'BP' suffix.


The Boilermate BP

When the Boilermate product was transferred to the Building Products division of Gledhill it underwent a major change. Taking a positive view of the changes one might argue that the product was improved by removing all the complicated technology required to run the older model.

As mentioned earlier, the Boilermate had become complicated and required microprocessor control for time functions, pump speed modulation, switching etc etc. By utilising a different type of heat exchange mechanism (an immersed heat exchanger) the new BP model no longer requires a store pump or the associated control.

Furthermore, where the older model controlled DHW output temperature by varying the heat exchange process (by modulating pump speed) the new model simply uses a TMV (thermostatic mixing valve) on the outlet to limit the temperature that hot water can be delivered to taps. Yes, it is great that a simpler way to achieve mains pressure hot water had evolved, but it came at a price.

How does the Boilermate BP differ

The concept of Boilermate was (in the early days) a total water management system that could deliver mains pressure hot water  and control the central heating. But things changed.

Not only did the Boilermate BP change how it created hot water (utilising an internal coil heat exchanger rather than an external plate heat exchanger) but it no longer had any control or function relating to the central heating.

Furthermore, the Boilermate BP was stripped of all electrical control devices (i.e. timers, electrical temperature sensors, pump controllers etc). From then on, all control devices would need to be provided externally.

(Please see Boilermate BP unit picture right - front cover removed)

The Boilermate BP would need to be incorporated by means of a traditional 'S' or 'Y' plan configuration - Just like a tradition copper cylinder might be.

New Boilermate BP unit with front cover removed. Note the simplicity of the connections!


The evolution continues...


Boilermate continued to evolve and passed through the BOILERMATE BMSCP model (seen right with schematic below), which was the first to utilise stainless steel in the construction. A hibrid of previous technologies, the BMSCP show the re-introduction of a plate heat exchanger for the DHW but incorporated a large boiler coil for heat input to the store.

BMSCP denoted 'stainless central plant'.



2020 - The Boilermate Stainless


2020 sees the Boilermate Stainless available in two types. The OV (a fully open vented model) for use in a fully open vented boiler and heating system. And the SP model that allows connection to a pressurised boiler primary circuit and radiator system. The store on  models of Boilermate continue to remain open vented and all models produce mains pressure hot water.



This model is pictured above. The most striking difference to models manufactured over the previous 20 years is the return to a cylindrical shape.

There is also a return to the days when a heating system could be run directly from the store (i.e. boiler heats the store, store supplies pre-heated water to the radiators). Mains pressure water still remains a primary function from an external plate heat exchanger.

The BMST OV is ONLY available as a 'pre-plumbed' unit. This is to say you simply hook up to connection points on the cylinder pre-plumbed by the factory during manufacture.


The BOILERMATE BMST can supply heating and hot water. It includes the brain to control DHW temperature and also the boiler and heating circulating pumps but boiler and heating controls (programmer) must still be added.



The SP Boilermate is still a vented thermal store, but can be used with a heat source such as a system boiler with a pressurised primary circuit.


Heat can be introduced to the cylinder from a pressurised primary via another plate heat exchanger (PHE). Now you have one PHE putting heat into the store and a second PHE creating hot mains water by extracting heat from the store. Meanwhile the store remains vented for maximum safety.

There is however a slightly different plumbing schematic (shown below) with which the boiler heats the radiators.

The BOILERMATE Stainless SP model is available in various sizes and as either a standard cylinder (shown above) or a pre-plumber version (shown below).


Although more expensive, the pre-plumbed Boilermate (PP) saves time on installation (simply hook up to pre-plumbed connection points). Cylinder includes pumps, zone valves and bypass.

Your heating system will require a programmer to be added (not included with either type of cylinder).



For further information on the newest addition to the BOILERMATE family please follow this link...













Alternatives to Boilermate

Now that Boilermate is simply a thermal store in a box, and because we know you will need to modify existing pipework during the process of replacement, you are of course no longer 'tied' as it were to the product. Replacement (if you wish to stay with the technology) will involve you buying a new thermal store (this is all a Boilermate is now) so you are at liberty to shop about.

In an attempt to keep things simple we will assume you wish to continue enjoying the benefits of mains pressure hot water together with the safety of an open vented thermal store. So which way should you go?

Top of the list must of course be to install a new type Boilermate BP. Perfectly understandable if you desire the cabinet style of the Boilermate BP. Just be sure you understand the differences between the new and old models and the alterations to plumbing and controls you will need to undertake. And remember, Boilermate BP is just a thermal store in a box. Nothing more.

If you are less concerned about 'the box' in which the Boilermate houses its store then you might like to look at a cylinder type thermal store.

There can be numerous advantages in considering a proper cylinder shaped thermal store. Not least is the fact that you can run heating directly from a cylinder type store should you wish in much the same way as the old Boilermate models used to. In short, cylinder type thermal stores are more versatile. Depending on the model you choose, cylinder type thermal stores will accept multiple heat sources simultaneously, provide mains pressure hot water AND remain open vented. They are therefore much more versatile than the Boilermate BP.


Which cylinder type thermal store should I choose?

Firstly you should take a look at the various options available to you. Gledhill (the manufacturer of Boilermate) make their own cylinder type thermal store called the Torrent Mulitfuel Store. Gledhill, in keeping with the company's propensity to brand their products with catchy names, have christened their thermal store cylinder with a name that describes the cylinder's function quite well. It is however only a thermal store and arguably does nothing more than other similar products.


You might also like to look at an alternative range of thermal stores that are available (follow the link for full info). These cylinder type thermal stores haven't been given snazzy names they simply perform the same function.


You might be interested to know that the Gledhill Torrent Multifuel store is available ONLY as described. The alternative cylinder however can be adapted and/or modified to customer specification and is available in cylinder and combination versions.


Thermal store cylinders can generally accept heat input from various sources such as solar, wood burners, AGA's, oil and gas boilers, air recovery and ground source heat pumps. The process is simultaneous, they remain open vented and all provide mains pressure hot water.


A thermal store is in some ways unique as it possesses the ability to accept heat from sources that are deemed 'uncontrollable' such as wood burners and AGA's. The inherently open vented nature of a store makes this possible without the risk of explosion.

Check them all out before you decide as there is often a price differential that cannot be ignored. You are always welcome to call our office for advice if the going gets a little tough!


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