Gaggia TS – Doesn’t Heat Up

I get quite a few questions about the Gaggia TS operation, mainly why it does not heat up.

I thought it would be useful to look at the electrical operation of the TS in some detail.

The TS User manual (Google search for Gaggia TS Full Manual TS 03-08-04.pdf) contains a wiring diagram (with a wiring error error in the region of the pump).

 gaggia ts wiring diagram

The first thing to look at is when the machine is first powered on.  No attempt is made here to copy the colours of the actual wiring by the way.

The mains power comes in through the IEC inlet on the underside of the machine (15) and is connected directly to the mains power switch (11).  If this is switched on, the neon should light up the switch, and power will be connected to the controller (13) pins 1 and 3.

The controller then monitors the level probes in the water tank (14) and if there is no water in the tank, the controller leaves contact K1 in a position to feed the front panel neon (1) to indicate the tank is empty.  The controller will do nothing else until the tank is filled.

When water is detected between the two plates in the water tank (14), contact K1 will changeover after about 1/2 sec.  For this reason, if you turn the machine on with the tank full, you will see the neon light for about 1/2 sec.

With K1 switched over, power is provided to one side of K2, and out of controller pin 7 to the coffee switch (10) so a shot can be pulled (see later).  Also at this time, the controller looks at the boiler probe (5) and looks for conductivity between this and the element earth wire.  If there is no conductivity, it assumes the tank is not full, and so closes K2 to provide power to the pump (12) and to the fill solenoid (9).  This allows the pump to pass water through the fill solenoid to the boiler.  The solenoid on the group head is not powered, so the pumped water does not reach the coffee.

If the probe is faulty, the boiler might overfill, so the controller only allows the pump to operate for a few minutes at a time.   When filling the boiler from empty, it will be necessary to switch the power off and then back on a few times to allow the boiler to completely fill.

When the probe detects the boiler is full, then contact K3 is closed.  This allows the heating element to receive power via the pressure switch (4).  This is a switch which is closed when the boiler pressure is below 1bar (14 PSI), and opens when it is above 1bar.  By opening and closing as the pressure rises and falls, the pressure switch can keep the boiler at the same pressure and hence also temperature.

To prevent the boiler overheating if the pressure switch fails closed, or if contact K3 fails closed even thought there is no water in the boiler, an overheat thermostat is wired into the heating circuit (7).

If the boiler is not heating, the quickest way to diagnose it is to connect a multimeter between points A and B.  You should see 230V AC.  If not, the controller is most likely at fault.  This sadly is the most common cause of failure, but is is quite easy to fix, costing around £65 for a controller which is just swapped with the original one.

If you do see 230V between A and B, then move the probes to between C and B.  If you don’t see volts here, then the pressure switch is most likely at fault (about £20 to fix).  To confirm this, move the probes to D and C.  If you still don’t see volts, then the over-temperature switch is probably tripped or is faulty.

But if you do see volts between C and D, then the element is probably faulty (£60 – £100 to replace).


The final stage is pulling a shot.  As discussed above, if there is water in the tank, K1 changes over and provides power to controller pin 7.  This feeds the coffee switch (10).

When this switch is closed, it power the pump (green line), and the solenoid on the group head (8).  This allows the pump to pump water through the heatexchanger inside the boiler, heating the cold water to around 100degC.  The piping then routes it to the solenoid, which now open allows it to run through the coffee.

Finally, there is an 80W cartridge heater (6) which keeps the group head warm via thermostat (2) whenever the mains power switch is on.


We now stock the following items to maintain the TS:

Group head gaskets and screens
Group head heater thermostat (98degC)
Steam and water taps and spare washers
TS Commercial Steam Wand
Panarello Wand
Pressure Stat (pressure Switch)
Control Unit
Pump (Ulka EP5)
Silicone hoses
Standard commercial and Bottomless portafilters
Orman kl.1.6 Pressure Gauge
Steam and water tap knobs
On/Off and Coffee Switches
Group solenoid
Fill solenoid

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17 Responses to Gaggia TS – Doesn’t Heat Up

  1. chris hanley says:

    hi stevie

    having a wee problem with my gaggia TS one. The steam seems to be stuck on, whenever it gets up to any pressure then the steam just comes out of the team wand, is there any areas i should be checking? many thanks


  2. chris hanley says:

    hi steve
    just finished puting machine back together after stripping down and cleaning and your plan seems to have worked a treat. many thanks chris

  3. Norman says:

    Hi Chris,
    Got my used TS at eBay to replace Classic. There is the problem – water comes out from ANTI-SUCTION VALVE (Nr. 13/14 from parts catalog) when heat up. Is this valve could be repaired or replaced?
    Thank you for any help,

  4. Martin says:

    Hi Steve
    If I switch my TS on it builds to 1.3 bar, make coffe then it slowly drops to zero. Turn it off for a couple of mins then on again and off it goes in the same cycle. I think it used to make solenoid type noise that re pressurised after dropping below a certain pressure. Any ideas and cost to fix. Plus what would a service for this machine cost?
    Thanks in advance

    • admin says:


      The pressure reading is the boiler pressure (used to provide hot water and steam only). When you draw a shot, this does not come from the boiler, but from the cold water tank, then through a heat exchanger in the boiler.

      If the pressure drops when you steam milk or use the hot water tap, then builds again, it is most probably just scale blocking the anti-vacuum valve.

      If it is working, when you turn the machine on from cold, after 10 minutes or so, you should hear the characteristic shssh of steam through the anti-vacuum valve for a second or two, just before the pressure gauge reading starts to increase from zero.

      If the valve is blocked, the machine pressure will drop to zero when the steam wand is used, but given time to recover pressure, will work fine all day.

      Let me know if you think this sounds like the fault. I know the symptoms are slightly different from your description.

      Otherwise, there are other possible causes.


      • Martin says:

        Hi Steve
        Just fired it up again and no shush just before pressure build stars so sounds like you may have hit the nail on the head.
        Machine has been stored for years so it likely it could be blocked can you point me to the part I need to look at. Is it remove unblock or replace? Thanks martin

      • Martin says:

        Found it on your blog. Will strip and de scale and try again

  5. Martin says:

    Hi Steve,
    Just taken the valve out its free so not the problem. Can you suggest other areas to check. Regards martin

  6. Martin says:

    After some more analysis the symptoms appear to be the following;
    Turn after boiler can be heard heating up, a short period pressure rises to 1.4 bar.
    Whether steam wand used or not pressure falls slowly to zero and does not increase again until turned off.

  7. Roger Widdowson says:

    Hi Steven

    What a brilliant blog! Incredibly informative.

    I have followed your troubleshooting as best as I can.

    When I switch on the unit, I get 240V to pin 1 on the controller but nothing to pin 3.

    It was working before it was put into storage some years ago and needed the group seal changing. Finally got around to doing this today.

    Switched it on and, like you describe, was nervous that it was going to burn out the element or explode or something equally catastrophic happen.

    Once I’d left it on for long enough (a good few nervous minutes) it cuts out so I then switch on the coffee switch and nothing happens. No water flow.

    I noticed there was a dicsonnected earth which appears to be from the valve / switch underneath the water tank at the back. Also, there is a disconnected earth where a tang has come off the casing from the IEC. The side and base are still earthed to the back of the IEC connector so that should be OK.

    Was wondering if you still sell parts?

    • admin says:


      It would really help if you could describe exactly what happens when you turn you machine on and what appears to be the fault. At the moment you question is similar to “my car is not working properly”.

      I am not clear from the question whether the machine heats up, what “it cuts out” means. However, I get that you have no water flow when you operate the switch on the top font panel. But some more clues please – do you hear the pump? Do you hear the solenoid switch?


  8. John Hodkinson says:

    where can I get a red on off switch for my Gaggia TS

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