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Discuss Worcester Bosch Heatslave Green star 18/25 continuously locks out in the Oil and Solid Fuel Forum area at

Since moving to our property in Dec 2017, the Worcester Bosch Greenstar 18/25 Heatslave, has had a recurring lockout problem, which 3 OFTEC engineers have not been able to diagnose/ resolve. Typically at night when on manual,with no hot water running and with NO HOT WATER demanded of it. The boiler will go to lockout and need to be reset by pushing the big red button.

Our last engineer replaced, 1.Photostat broken, 2- an ignitor broken, 3 fuel pump, 4 - solenoid coil, 5 - the control box. After replacing the control box boiler worked 4 weeks without fault occurring. Then last night boiler went to lockout again!

In desperation I Googled problem and found at least 2 other people reporting same issue, with no satisfactory answer other than 'It could be any number of things' OR 'If your OFTEC engineer cannot fix it call Worcester Bosch to fix it.

So//I called Worcester Bosch tech line and explained problem in detail, explaining all major components changed apart from water pump,expansion vessel, known to be fine as was the Diverter valve.

The 1st thing Worcester state to as emphatically the most probable cause of the problem is:

*Does your fuel have additives added?'

To which I respond in the affirmative, as the oil seller 'carte blanche' recommends customer's add additives to enhance performance of boiler. However, Worcester Bosch, stated to me categorically, that the lockout problem was likely to be happening because of the additives!

I then called my latest OFTEC engineer and told him what Worcester Bosch had told me about the Heatslave 18/25 SHOULD NOT have any additives to the fuel - He said he had never heard of this advice before and was unaware that fuel additives would cause the 18/25/a problem!

I then called Worcester Bosch back again and asked a different technical representative to confirm the problem IE: That the 18/25 should NOT HAVE any additives added to fuel?

The 2nd technical representative for Worcester Bosch again confirmed this advice. I then asked the Technical Representative, whether at any time (past/ present) that the boiler manual for the 18/25, has stated OR currently states 'DO NOT PUT ADDITIVES IN FUEL?'

The categorical response from the Worcester Bosch representative was the manual AT NO TIME in past or indeed the present, stated/ or currently states/ THAT: ADDITIVES SHOULD NOT BE ADDED TO FUEL.

I therefore suggested to the Worcester Bosch representative, that it might be a good idea if THEY PUT THIS IN THE MANUAL! Or clearly put the advice somewhere as many, many people will be getting the same problem. Their technical representative then accordingly stated he would pass on this feedback higher up his chain of command, so it can be published in the 18/25 manual and perhaps the summary sheet as well with boiler/ along with widely publicised on the Worcester Websites and Forums. *(Would be a good idea also).

I then called back my OFTEC Heating Engineer, whom again was very surprised that fuel additives would cause repeated Lockouts. If this is the case, then, suspect same would be case for every OFTEC engineer. would not be aware, the last three engineers, coming up with the root problem of additives to the fuel being the main problem.

Currently Worcester advise that the problem, is likely to keep occurring for potentially, until my current and another (1/2) complete tanks of oil (additive free oil) has gone through my boiler!

My heating engineer, pointed out that this was all quite a big deal and was likely be causing a major headache for people whom have oil burning stoves and an oil fired boiler, as the stoves he says, HAVE to HAVE additives and generally speaking both STOVE and BOILER will be fed from same tank!

Consequently to summarise. If your Worcester Bosch, Heatslave, Greenstar 18/25 continues to lock out, no matter how many Heating Engineer call outs. Then if you have put additives in the Fuel Tank to improve the performance as generally recommended by the Oil Seller/then the 18/25 cannot cope with the additives.!

However, Worcester Bosch have at no time published this advice in the 18/25 manual! Other than the Worcester Bosch"s manual states that the 18/25/should run on 28 Sec Kerosene only!

That is all at present.

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