worcester 15/19 heatslave domestic hot water not working

[byron the dog]

Hi, Hope someone has come across this before.

1) Boiler make / model (gas or oil) - worcester 15/19 heatslave oil

2) What is / is not happening - CH OK, no hot water

3) Has ANYTHING else been done / changed recently - turned off CGH for summer (switching it back on does not help)

4) When did it (problem) start - week or so ago, no trigger event

5) When does it happen? eg, heating coming on or going off - permanent problem

6) Anything else you feel may be of relevance - CH OK, water pressure low, suspect not triggering flow switch, if I jump flow switch contacts on PCB then pump works and burner kicks-in. What diagnostic test can I do to work out if it is lime-scaled HX causing problem or flow switch is faulty (had multimeter across it and it does not trigger when hot water tap is turned on.

So, which one to go for HX or flow switch and how to go about briefing an engineer.

thanks

 

[ChrisR]

What's the actual flow rate, in litres/minute?

 

[byron the dog]

2l/min

 

[oilman]

If the cold water flow is ok, then it's the heat exchanger. If you get some fibre washers then you can follow the instructions in the book to remove it, descale it (no instructions) and re-fit it. Add a Combimate to the supply to the boiler to prevent it happening again.

 

[byron the dog]

thanks, I see, section 19 "replacement of parts" para 8. You are right, no instructions on de-scaling, any thoughts?

 

[byron the dog]

And, on reading further, I notice that there are no instructions on how to drain the boiler. It says somewhere that the CH pipes shoudl have valves enabling easy serviceing and, as you can guess, there are none. So, do I have to drain down the whole CH system to drain the boiler and either way has anyone any advice?

thanks in advance

 

[Gasguru]

If the cold water flow is ok, then it's the heat exchanger

What about a blocked inlet filter to the flowswitch? or more likely a blocked flow restrictor on the flowswitch outlet.

Probably uses the standard type in which case remove the O ring.

 

[byron the dog]

Thanks, already stipped and cleaned the flow restrictor and flowswitch (I needed to check it worked if I flicked the paddle manually and it does) and they were fairly clean anyway. Mains inlet pressure OK too. So, I'm going with the HX, just need to work out how to drain boiler

 

[Gasguru]

Yes they might be clean but the O ring can swell up and reduce the flow - hence remove it.

 

[byron the dog]

will have another look at this then thanks

 

[ChrisR]

Haven't even looked at the instructions but just as an - if you're adept at getting into the cw input which it sounds you are, you could rig up a funnel/hose etc to get descaler in. Washing machine hoses... garden sprayer...
Saves draining the boiler and dismantling.

 

[byron the dog]

like your thinking, I had already been thinking along the same lines, just wondering what to use to get the scale off when whatever I shove in is going to have to be cold and cant really be pumped in. Anyway, busy next few days and then cricket tour at weekend so, will sit and think about it some more before doing anything else

 

[wilhelm]

why not fit a new hx....

enjoy the tour.....

 

[ChrisR]

Best stuff is fernox DS-3 (sulphamic acid) for limescale, though citric (DS-40 works too and would be better on the primary side.
It can be very hard to get all the limescale out though.
Looking a the diag it's an easy one to remove

Warm it up with boiling water in the other side.

 

[wilhelm]

why fekk around.... ?

ask worse cester boshhhhhh tech help line. theywill tell you the good news. with knobs on