Hi there to anyone who can possibly help me with the above problem.

The boiler works fine for central heating, the problem is with hot water. The boiler is very hit and miss lately with firing up when a tap is opened. Sometimes it works fine at other times
I find that a gentle knock with a spanner on the mains cold water inlet pipe gets it to fire up when a hot tap is open.

We have been away on holiday and this problem has developed since we have been back, over the last few days. The heating was left to run as normal program, but no taps were in use.

I wonder if some crud has managed to block the operation of the flow detector on the mains inlet? Is this feasable?

If so, can the detector be removed and cleaned and reinstated? Is it a screw thread to remove it?

I have over the time we have had the boiler replaced two ignition PCBs and one main PCB, when the auto-vent let water pass and it ran down the cables onto the PCB connections. What a good design.
Needless to say the auto-vent has been replaced each time.

If the above assumption is incorrect, any other suggestions as to the cause/fix would be appreciated.

Thanks in advance for any possible solution/knowledge.

Tonynat, May 2008

The heating works fine, but the hot water is not very hot.

Enid, October 2012

boiler will not fire up fan comes on but no gas ignition and no green light

neil short, March 2012

Update, boiler working fine, found both the gas board and the water board laying new mains round the corner!

Still think I need to clean the flow switch for good measure. Thanks for that.
The 'auto vent' is the auto air bleed on the top of the boiler.
Having had a safety valve blow on an old previous boiler, I can confirm that it piped to outside!

Back to the dhw flow switch - dismantling the boiler is no problem, but knowing which way the thread turns to undo could be a problem, as I often don't know my own strength when wealding a spanner. I know the normal way of threads, just seems that this one might be different?

Thanks again for the help T

Tonynat, July 2008

Yes, it sounds like the dhw flow switch has cruded up, you will have to drain the boiler and dismantle it, then use something like some copper wire to unblock the orafices, possibly may need to change the diaphram if it looks worn or split.

The 'auto-vent' as you call it, do you mean the 3bar safety valve? if so, this should only lift if the system has a problem (resulting in too much system pressure) and also it should be piped to outside to vent!

T, May 2008

Note to the above question, we live in Bristol and we have noticed that at peak demand times (7.00-8.00am) the bolier sometimes doesn't fire on the hot water tap. I was wondering if this was because of a reduced mains pressure in the area and if anyone else in the area had suffered similar problems?
It only seems to have happened since 'The French Company' has taken over Bristol Water. Could this reduced pressure generally be to avoid mains leaks?

Tonynat, May 2008