Halstead Ace High Combi Boiler - Overheat and Lockout

We have a Halstead Ace High. Within about 45 seconds after drawing a substantial amount of hot water (two showers) the boiler will start spitting out steam and hot water droplets from the little rectangular hole at the top-left (I've taken the front plate off). It will then usually lock out the next time we draw hot water.

Had a guy in who said it was probably the little switch getting stuck in the 'on' position and causing the boiler to overheat. He was talking about a chrome pin that comes out of the big brass unit near the bottom and activates a relay-type switch inside a little plastic box (sorry, I don't know the proper names). We investigated this and it turned out not to be the case. In fact, the pin does go back (although slowly) and the boiler seems have successfully turned off, but then 45 seconds or so later, the spitting/steaming starts.

We've had an engineer in and he wants to replace the whole Diverter Valve at a cost of almost £300. With a baby on the way we could really do without this!! I know nothing about boilers but am generally pretty smart and handy, so would like to seek alternatives or at the very least understand more before forking out this amount of money.

Would anybody be able to suggest any alternative advice and even possible cheaper courses of action?

Your help is much appreciated!

Andy T

First of all run the heating, does it do the same on heating let it run and get to temp and shut down itself as it should

If heating is ok, run the hot water, when you turn the tap off does the orange burner on light on the front facia stay on, when it goes to lockout, even though the tap is off?

Get back 2 me with this info, we can take it from there

Hi Ollie,

Thanks so much for taking the time to answer my question. I really appreciate it.

Do you want me to test whether the heating causes a steam/spit episode (which, on current evidence, I don't think it does) or whether the heating can cause a lockout AFTER a steam/spit episode (which it might)?

99.9% sure that the burner is OFF when a steam/spit episode occurs. I will verify this and get back to you.

Thanks again mate.

Just run heating ans see weather is causes anything abnormal to happen with boiler and let us know

If the burner isnt staying on you can almost certainly rule out spindle sticking and causing dhw micrswitch 2 make, thus keeping burner on, this is what your RGI was getting at, and you can get a service kit if it was that, which is doesnt seemto be, at a fracton of the cost of a full diverter valve

Does it only happen when CH/HW is tuned off, and can you tell if pump continues to run after a demand (by removing large screw in middle see FAQ'S) might not be over running to disperese the latent heat, the over run is built into PCB's on these, ive had the exact same fault on a model of the ace (a later one) replaced PCB and pump over ran and boiler stopped O/HTG

Hi Andy, did you ever resolve your over heating problem?

I've got a Ace High doing the same thing - Locking out and over heating when we have a shower. I've a feeling my PCB or the thermostats are at fault because if you turn the thermostats down, it still overheats. The pump seems ok and was replaced a couple of years back for another issue.

The problem I have now is that the AAV seems to have a problem as it's weeping water. I guess because as all the overheating it's had to vent.

My plan is to test the thermostats at the weekend and replace the weeping AAV. If the thermostats seem ok, I guess the only thing left would be to replace the PCB.

Am I on the right lines?

Thanks

Julian