Brand new Bosch boiler keeps overheating - help!!

[Sten]

Hi

I recently got the plumber in to undertake a power flush of my CH system, he advised that my boiler had to be condemned and I've since paid out 4 grand for a new Worcester Bosch boiler. Great.

My problem is this - the boiler keeps overheating and cutting out - we set it to come on at a specific time, get in from work and find the rads are cold and the 'overheat' light on the boiler is lit. The plumber said that the pump was oriented the wrong way up, and so may be letting air in to the system, hence creating an airlock in the pump causing the heat to build up in the boiler. Today he has been to turn the pump round and lo and behold, the same problem is still occuring! If you turn the temperature knob on the boiler down and then back up again, the overheat light goes out and the rads start to warm up.

Can anyone help? I'm not sure of the model number of the boiler but can check later and add to the post tomorrow. I'd really appreciate some advice as I'm starting to wonder whether this plumber has ripped us off...

 

[taydo]

HOW MUCH

Where do you live what did he do

keep calling him back until you have it fixed.

only he knows what he has done

 

[boilerbeasty]

Four thousand pounds ?
I'm sure the boiler looks nice though, with all the gold leaf on it.
Well I don't know what you got for your money, but the very least it should do is work.

 

[wireman46]

No doubt about the rip off!

I had this problem with a Halstead a while ago. This boiler had a low-capacity heat exchanger (this is design, not a fault) that required a good flow of water through it. Pumping the water round the whole central heating system was too slow for it; the water in the heat exchanger reached close to boiling and then tripped out necessitating manual intervention to restart.

Basically, this boiler would work OK if enough water moved through the heat exchanger so it could heat it up and the pump could move it on before it got too hot. When the incoming water (return) was at a high enough temperature, the heat exchanger would turn off, the pump would still circulate the water and when the return temperature was low enough, the heat exchanger would start up again.
All this has to happen at a temperature below that when the safety over-heat cut-out operates. If the water flow is too low, the safety cut-out works quicker than the heat-exchanger turn-off (and so it should!) and the boiler shuts down.

Solution (from the Halstead documentation) was to insert a bypass connecting the boiler flow to the boiler return. There was a control cock in the bypass allowing adjustment to the flow that was allowed to bypass. I placed the bypass next to the motorised valve (between boiler and valve) which was adjacent to the hot water tank and in pipe length, about 3 meters from the boiler, which happened to have the pump next to it. Radiators started to connect to the flow/return after this 3 metre point.

Result was that the pump could move enough water through the heat exchanger to allow it to heat up the water and move it on before the overheat tripped. Not all of the water took the bypass route so the rads still heated up in the normal way - they might have taken 5 minutes longer.

It would be good practice also to ensure that the control system is configured to make the pump over-run (i.e. continue running for a minute or two after the heat exchanger decides it wants to stop heating for a while).

Possible alternatives: fit a new, more powerful pump that keeps enough water circulating and avoids the problem; do a drain/flush - how much sludge do you have in the system that might be slowing down the flow; ask for a refund and get a decent plumber

Good luck.

 

[COG]

Have you contacted Worcester to chack out the boiler , you did say it was brand new

 

[taydo]

hi if thats the case wireman
he could probably try turning the pump up first if the controls are there of course?

 

[DP]

Original post says boiler is WB only. No model nothing.

I suspect the boiler is a combination boiler. Pump is integral. These boilers are 'fired up' to carry out assembly line tests. I have never come across a pump fitted the wrong way around. This is not to say it cannot happen, only that it is unlikely in light of the fact that reversing the pump has made no difference.

Is the fitter CORGI Registered AND has he got a CH ticket? Has he commissioned the boiler- for this see the benchmark logbook (which should have been completed by the fitter as well as the commissioning engineer). which you should have been given along with installation manual.

I think the poster needs to take drastic action to get the boiler repaired. If he does not have the benchmark logbook, system has not been cleaned or the defect is installation related, the makers may not want to know.