Lockout on Worcester Heatslave 12/14

[Happy Harry]

I have a Heatslave 12/14 with the oil tank about 6m higher than the boiler so the supply line is fitted with a pressure reducing valve at boiler level. These valves seem to have a life of about 3 years before they resrict the flow to the extent that the boiler locks out. I am now waiting for delivery of a new pressure reducing valve but find that a sharp tap with a spanner on the body of the valve will get the flow going again for a day or so.
Following my last 'tap on the valve' I bled the fuel line via a pressure gauge screwed into the oil pump. The boiler fired up but locked out after a few seconds. I traced the fault to the photocell that was loose in its plastic housing and I may have inadvertently pulled it partly out. The photocell was quite clean and after pushing it back fully into the housing we had heat once again for a few hours before the next lock out.
On the next lock out there was still a good flow of oil, the photocell was still in the correct position, on resetting the lockout button the oil pump starts immediately and delivers a very steady 100psi, the air blower fan starts immediately, but there are no further clicky noises from the burner control box, the burner does not ignite and lockout occurs in 20 seconds.
Anyone got any ideas please.

 

[SimonG]

control box / solenoid hard to say without it being in front of me.

 

[Happy Harry]

Thanks Simon.
Turned out to be the solenoid. It was open circuit so I checked the resistance of a solenoid from an old pump. That turned out to be 2000ohms so I changed them over and hey presto, it works!

 

[SimonG]

The coil breaksdown when it heats up and locks out, 20 minutes later it will restart, but only till warm and the cycle repeats until replaced.

Glad you got sorted.

 

[Happy Harry]

Still going strong Simon. The house had got pretty cold so the boiler was going hammer and tongs yesterday afternoon and last night.
Yes, exactly as you say, coils can break down as the temperature rises and come alive again when things cool down. Obviously if there is a break in the wire then it seperates as the coil expands and makes contact again when it cools down. I once had a similar problem with a relay. All the symptons pointed to a duff relay but the contacts were bright and shiny and in perfect condition. The problem was indeed the relay energiser coil that was OK for about 20 mins and then off and on intermittently. These sort of faults make diagnosis difficult but it is worth putting it away in the 'experience' file.