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Heatslave 15/19 hot water problem

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  • Heatslave 15/19 hot water problem

    Hi there,

    I have a Heatslave 15/19 oil fired boiler. Lately there has been an intermittent problem and at the same time be a constant problem. When the central heating is on I cannot get hot water. When the central heating is off sometimes I can get hot water sometimes not. When there is no hot water I can press reset and then the boiler fires up and I can get hot water.

    I have done some investigation and have spoken to Worcester by phone speaking with their technical help line, but I am still confused.

    Here are the facts.....

    When I switch the central heating on the unit functions as it should except I can get no hot water.

    When the central heating is off and at times when I cannot get hot water I hear water running though the system. If I press the reset the boiler will fire up and I can get hot water. At this point I was thinking the 3 way valve was knackered.

    I have had an engineer round (not a Worcester one) and he later spoke with Worcester as he was not sure what was the cause of the problem. He then asked me to check if the central heating functioned, if it worked and no hot water then this meant the PCB needed replacing. However he will not guarantee to fix the fault (as Worcester would prefer there own engineer to confirm but the nearest one is over 1 1/2hrs away) and he will not do sale or return on the PCB if it fails to fix the fault.

    Since this is an expensive fix I called Worcester help line to have some confidence that this would remedy the fault. The engineer on the end of the phone thought it was more than likely a fault of a flow switch.

    Anybody out there with some pointers as to what the problem is?

  • #2

    I'd certainly be looking at the flow switch before I looked at anything else as it's a common fault on the heatslaves.

    One way to check for an intermittent switch is to stand by the boiler and get someone to turn a hot tap on. If you hear a click from the top of the boiler, the boiler fires up and you get hot water then the switch is operating correctly. However if it doesn't make the click sound and there's no hot water then the switch is at fault.

    Go through the same process as you have been doing to get hot water and listen out for that click, take a note of what's happening.

    If you are finding that the switch is making that click regardless of getting hot water or not then I'd have to start looking at your control box on your burner. Neither of these problems are expensive to remedy, flow switches range from 30 to 80 depending on the serial number of your boiler and control boxes are roughly 50 to 100 depending on model (you should have a satronic control box which are reasonably priced) and if your engineer is charging more than 2hrs labour to fit then he's taking the wee wee!

    Let me know your findings with your test



    • #3
      Thanks for the advice and will give it a try and will report back. I am used to flow switches opearting in control systems but without the relevant drawings of the unit I cannot fully understand how the boiler operates.

      I take it this flow switch monitors the flow going to the hot water taps only? If correct then turning a hot tap on, it will monitor the flow passing through the pipe then will send a signal to fire up the boiler?

      What does the flow switch in this boiler look like?



      • #4
        Yeah, you've kind of got the idea. The hot water system on a combi is a sealed system and your hot water pressure is dictated by the pressure of the cold water entering the boiler. The flow switch is situated at the top of the boiler (on the left I think) and is on the cold water supply entering the boiler. If you lift the top of the boiler casing off and trace the cold water supply into the boiler you will see a compression fitting with either a black or red plastic nut and switch coming off it, it's T shaped with the switch on the branch.

        When you turn on the hot tap you open the seal of the system and the boiler takes in a cold feed at the same rate that the hot water comes out. The pressure of the cold coming in flicks the switch (it has a paddle type affair that sits at the bottom of the switch which is situated in the pipe) the switch then sends a signal to the control box which in turn sends a signal to the fan and burner requesting the boiler to fire to heat the incoming cold water.

        Hopefully that's made sense, I'll try and look out a link for you for a flow diagram of the boilers electrics, if you can follow flow diagrams and are confident testing electrical terminals you'll soon see what's wrong with the boiler.......unfortunately it's not something I'm able to do from this computer!

        Let me know how your tests go and I'll do my best to help you through the test procedure.



        • #5
          I have been testing the boiler for the past few days. I have located the flow switch (a red thing on the LHS of the boiler underneath the lid). When turning on the hot water tap there is an audible click and the boiler fires up no problem.

          When I switch on the HWS things are different. When I turn on the hot water tap there still is the audiable click but the boiler does not fire up to heat the water (though it manages to keep the radiators hot). When the central heating goes off, and turn the hot water tap again there is a click but no hot water. There is a discernable noise of water running through the boiler but the boiler isn't doing anything. After a good few hours there may be a chance the boiler will heat the hot water sometimes not. If all else fails I have to press the reset swich to get the hot water back on.


          • #6
            Thanks for all the extra information, hopefully we can get to the bottom of the problem now.

            It sounds like it's your diverter valve. This is the device that allows a combination boiler to heat both the hot water and central heating without the need for a hot water storage tank. This device is nearly always mechanical and is prone to breaking down.

            A good way to test if the diverter valve is breaking down is to turn off the boiler for 2-3 hours then switch the boiler on but on the summer setting only (meaning the boiler should only give hot water).
            Run the hot water tap at the bath and leave it running for 5 to 10 minutes or until the bath is full.
            While the bath is being run see if the central heating pipes under the boiler are getting hot or check if the radiators are starting to warm up if you dont know which are the central heating pipes under your boiler.

            If this happens, and I'm guessing it will, it'll be the valve for sure. Can you take a picture of it for me? You can buy just the motorized heads for some of them and replacing the head is a nice easy job.

            If you have an installation manual you'll find a diagram of the boiler on page 7, the diverter valve is number 3. Get me a picture of it and I'll see if the head can be bought seperately from the valve body.



            • #7
              Finally managed to get some time to switch the boiler off (had to work round family).

              I did as you stated and ran the hot water for ~10 mins. There is a hot pipe (marked on the photo with the white rod) which gets hot. Now this pipe feeds the radiators. Only thing stopping them heating up is the actuated valves which controls hot water feeding the radiator circuits.

              I have also uploaded a picture of the 3 way valve. Summing up does it all indicate the 3 way valve
              needs replacing?


              • #8

                Yes, it sounds like the 3 way valve is passing as the heating shouldn't be getting hot at all if there is no demand for it.

                Unfortunately it's a bit of a sod of a job and I'm not sure the head alone can be replaced on your type. I'll have a look and get back to you.


                P.s Your boiler is a combi right? Produces heating and hot water?


                • #9
                  Thanks for you help you are right it's a combi.



                  • #10

                    Did you manage to fix this problem? I have a Heat Slave 20/25 with a very similar fault - no hot water, with or without the CH on, and radiators getting hot when the hot water is on. I think the diverter valve is most likely but I also wondered whether the pump should be running when the CH is off but the boiler is going?



                    • #11
                      I am no expert but it sounds that you have the same problem as me. No doubt you'll have tried the various suggestions on this thread to narrow down the fault. If the valve is partially open (like mine) the hot water is going through the easiest way round your house, which in this case is your radiators. I can get hot water but only when the CH is off. I have actuated valves on two circuits that feed the rads, so although the diverter valve is partially open the hot water can only go as far as the valves in the CH runs (about 3 foot away from the boiler), so the water has to go through the taps.

                      Although I have not yet replaced the diverter valve, (due to the mild weather), phone up Worcester. Ask for their technical help department and they will tell you the part you need.

                      Not sure about the pump angle you mentioned. If it's a combi boiler it works off the mains pressure, and the noise you hear is the boiler firing up to heat the water......that said I am no expert!


                      • #12

                        I seam to have the same problem with my 15/19....No hot water and radiators getting hot with central heating turned off. I have it turned off at the moment waiting for it to cool down for a few hours.

               mention that you get hot water when you hit the reset. I get the same results after hitting the reset. How have you forced the flow through the HW heating?

                        Have you replaced the valve and did you have to get the valve body or did you manage manage to get the actuator separately? (assuming that it's the actuator that's faulty and not the brass valve). How can I test whether it's the actuator or the valve?

                        Do I need to drain down the system to replace the actuator?

                        Any other tips would be gratefully received.

                        Many thanks in advance.


                        • #13
                          Hi there, don't know if I'm in right place here asI am new to this forum. I have a heats lave 15/19 Worcester and the water has intermittent fault. Sometimes it's ok, next time it can be scalding hot. It's a council property and engineers have replaced hot water stat 3 times with no resolution to problem. Last engineer reckons its heat transfer from heating side but surely this wouldn't be possible. Would it? Any suggestions much appreciated in advance. Heating works as it should.