The original Gulfstream is an early example of the thermal stores that Gledhill specialise in making. I'd estimate these were made between around 1985 and 1995 but there are very few still left in regular use. Unlike their other thermal stores, the Gulfstream is self-powered by gas. It incorporates small gas-fired water heater inside the casing which heats the store water.
Like conventional hot water cylinders, a thermal store is a container filled with hot water but here the similarity ends. Once filled, the water in a thermal store never changes. Instead, the hot water stored in it is used to heat the tap water using a heat exchanger. This allows the hot tap water to be delivered at full mains pressure, and is one of the primary benefits of installing a thermal store instead of a conventional hot water cylinder. For central heating, the hot store water is pumped directly around the radiators.
The original Gledhill Gulfstream transfers heat into the tap water using a coil of pipe immersed in the thermal store water. Cold mains water flows through this coil of pipe and is heated through the wall of the pipe and emerged hot, for delivery to the hot tap.
Central heating is very simple in that the CH pump starts and circulates the thermal store water around the radiator circuits whenever the CH timer and room thermostat are both calling for heat.
What IS a Gulfstream 2000?
The Gulfstream 2000 is a another example of the thermal stores that Gledhill specialise in making. Unlike their other thermal stores though, the Gulfstream is self-powered by gas. It incorporates a high efficiency condensing gas boiler inside the casing which heats the store water.
Other than having a gas boiler built in, it is pretty similar to all the other 2000 series Gledhill thermal stores.
Like conventional hot water cylinders, a thermal store is a container filled with hot water but here the similarity ends. Once filled, the water in a thermal store never changes. Instead, the hot water stored in it is used to heat the tap water using a heat exchanger. This allows the hot tap water to be delivered at full mains pressure, and is one of the primary benefits of installing a thermal store instead of a conventional hot water cylinder. For central heating, the hot store water is pumped directly around the radiators.
The Gledhill Gulfstream transfers heat into the tap water using a pump and an external 'plate heat exchanger'. A plate heat exchanger is a block of very thin stainless steel plates arranged so that cold mains water can flow through one set of spaces between the plates, and hot water from the thermal store core can flow through an alternate spaces. Heat transfers through the plates and heats the cold mains water on it's way to the hot tap.
How does the Gulfstream 2000 work?
The integrated condensing gas boiler heats the water inside the thermal store. A thermistor (heat sensor) is attached to the domestic hot water outlet from the plate heat exchanger. When the thermistor records a fall in temperature it knows a hot tap has been turned on and the circuit board runs the pump. The pump circulates stored hot water through the plate heat exchanger, heating it, and the circuit board turns it off again when the thermistor reports a temperature rise. This system is proportional. The bigger the temperature fall seen by the thermistor, the faster the circuit board runs the pump. This way the designed flow temperature can be maintained at almost any flow rate when a hot tap is turned on. Central heating is very simple in that the CH pump starts and circulates water around the radiator circuits whenever the CH timer and room thermostat are both calling for heat.
Common problems:
1) The red "Store Overheat Lockout light" keeps coming ON.
This is time-consuming and expensive to fix properly because a new gas-to-water heat exchanger is required, although there is a cheaper 'get it going today' bodge that usually works for a short while (but is obviously not guaranteed!) The heat exchanger in the integrated gas boiler becomes contaminated with products of corrosion if the correct corrosion inhibitors are not added to the circulating water by the original installer. This restricts the water flow though it allowing the top of the heat exchanger to overheat. One, or both, of the overheat protection thermostats trips and the unit stops working until the user re-sets them. Then the cycle repeats. The unusual cylindrical design of the heat exchanger means that the corrosion deposits cannot be effectively removed by chemical or powerflushing treatment, so a new heat exchanger has to be fitted.
However, the fault is likely to return unless the system is also powerflushed or otherwise cleansed and the correct corrosion inhibitors added. This adds up to an extremely expensive repair. You'll have to employ a heating engineer or powerflushing specialist to carry out this additional work. Many owners decide to fit a new boiler rather than repair a Gulfstream with this problem. This problem is compounded on many Gulfstream installations when the radiator systems are connected using microbore tube (thin pipes about the thickness of a pencil) because microbore systems cannot be effectively powerflushed. If a heat exchanger is replaced on a Gulfstream connected to a microbore heating system Would also recommend employing a plumber to remove each radiator and flush it individually, or alternatively, replace all the radiators with new ones. Whatever cleansing method is used it is difficult to remove products of corrosion from heat store in the Gulfstream so would suggest fitting a magnetic filter to the system. This will maximise the life of the new heat exchanger by capturing any corrosion debris remaining in the circulating water.
2) Red "Ignition lockout" light coming ON.
Pressing the "Reset" button makes the light go out, but fails to start and the light comes back ON again after a short wait. This is failure of the flame to light. I've seen this twice now caused by pre-mix fan failure. The impeller disintegrates and the debris simply jams the fan and stops it from rotating. A new pre-mix fan fixes the problem. The "Ignition Lockout" light coming ON can also be caused by an absence of gas, failure of the ignition module on the gas valve, or the condensate trap (or drain line) being blocked.
3) Leaking pump isolation valve leading to pump failure.
The pumps fitted to Gledhill appliances (sensibly) have isolation valves fitted, so failed pumps can be replaced without draining the whole system. Not so sensibly, the type of valve used is the 'ball' type which tends to leak after a few years. On a 'ball' type valve there is no packing gland to tighten so as the leaks can't be fixed except by draining the system and replacing the whole valve, so as the leaks are small they tends to be ignored. Unfortunately though, the water drips onto the pump and eventually finds its way into the pump motor windings, causing the pump to fail. Of all the Gledhill range of appliances the Gulfstream 2000 seems especially prone to this problem.
4) Pump failure leading to control board failure.
When any of the three pumps in a Gulfstream fails it tends to damage the electronic control board. This is an expensive board to replace.
5) Thermistor failure.
The heat sensors (there are actually two) can become unreliable with age. This usually presents as unpredictable hot water performance or unstable hot water temperature. The thermal store will be hot, but the pump will not run fast enough (or at all) when the hot tap is open leading to warm water from the hot taps degrading to cool and staying cool, or simply running hot/cool/hot/cool/hot/cool and driving users to distraction.
6) Central heating timer clock failure.
The clock appears to work correctly but the switch inside fails to operate. The CH remains permanently ON (or OFF).
7) Water scale-contaminated plate heat exchanger.
The plate heat exchanger is prone in some areas to water scaling. This presents as maximum water temperature becoming progressively lower, and in the final stages of scaling, the flow rate from the taps reducing too. The fix is to either fit a new plate heat exchanger, or to de-scale the existing heat exchanger using conventional descaling techniques.
8) Central heating failing intermittently.
Usually caused by triac failure on the main control board. A new board will be needed.
9) Central heating failing to turn OFF.
Once timer clock failure has been ruled out this is usually caused, once again, by control board failure. A new board is probably required.
10) Water dribbling from the overflow.
Usually caused by the automatic filling device (RPZ valve, or 'CA device') failing to close properly and discharging through the safety discharge pipe. A new CA device will be needed. They cannot be successfully repaired in my experience.
11) Concealed flue duct not accessible for safety-checking
In addition to the long list of problems above, many Gulfstreams have potentially defective flue installations. To be more precise, many Gulfstreams have long concealed flues that cannot be visually inspected and therefore cannot be verified as safely/correctly assembled/installed and safe to use. Anyone working on a gas appliance is required by law to examine "The effectiveness of any flue". Not being able to visually inspect the flue presents quite a problem as the technician, according to Gas-Safe, needs to satisfy him or herself that the flue is both continuous throughout its length, and properly jointed & supported.
CORGI/Gas-Safe have issued a Technical Bulletin (TB200) giving details of how to install and safety-check these long flue ducts. TB200 requires builders to install inspection panels along the length of a concealed flue duct. TB200 also accepts that many boilers such as the Gulfstream have been installed without these inspection panels and therefore cannot be visually inspected, in which case a 'risk assessment' must be carried out. TB200 goes on to define the steps in completing the Risk Assessment but whatever the outcome, a Warning Notice must be issued classifying the installation as "Not to Current Standards", or possibly "At Risk" or "Immediately Dangerous".
What IS a Gulfstream A-Class?
The Gulfstream A-Class is Gledhill's latest version of the Gulfstream, and represents a major 'ground-up' re-design of the appliance. Many of the problems with the Gulfstream 2000 have been addressed but the unit is too new for me to have much experience of repairing.
The unit is a thermal store, but unlike Gledhill's other thermal stores the Gulfstream is self-powered by gas. It incorporates a modern, high-efficiency condensing boiler inside the casing which heats the store water.
Other than having a gas boiler built in, it is pretty similar to all the other Gledhill A-Class thermal stores.
Like conventional hot water cylinders, a thermal store is a container filled with hot water but here the similarity ends. Once filled, the water in a thermal store never changes. Instead, the hot water stored in it is used to heat the tap water using a heat exchanger. This allows the hot tap water to be delivered at full mains pressure, and is one of the primary benefits of installing a thermal store instead of a conventional hot water cylinder. For central heating, the hot store water is pumped directly around the radiators.
The Gledhill Gulfstream transfers heat into the tap water using a pump and an external 'plate heat exchanger'. A plate heat exchanger is a block of very thin stainless steel plates arranged so that cold mains water can flow through one set of spaces between the plates, and hot water from the thermal store core can flow through an alternate spaces. Heat transfers through the plates and heats the cold mains water on it's way to the hot tap.
Central heating is very simple in that the CH pump starts and circulates the thermal store water around the radiator circuits whenever the CH timer and room thermostat are both calling for heat.
