Worcester 24i- no CH or HW for 5 weeks

[queenb]

Our 2 year old worcester 24i has been playing up for quite a few weeks now and we are cold! We have had two engineers out to look at it and a new PCB, thermistors, gas valve put in, but to no avail.
At first the fault was intermittent. The HW worked, and the CH would come on and then cut out within about an hour , only coming on again if we turned it off at the wall and then turned it back on. Gradually this got to be within 2 minutes and then it cut out, and we had to wait about an hour before it would come on again once turned back on at the wall. Now the HW isn't working either- the same thing happens. The flame lights for less than 2 minutes, and as soon as the hot water starts coming through, it cuts out and won't relight.
There is no variation in the cooker flame when the boiler is trying to light.

Once the engineers had replaced all the bits mentioned above, they now say it must be sludge in the radiators causing it. We have been unable to get the rads off to empty them, as they are stuck on tight so have a plumber coming this week to clean them out for us.

My question is any ideas what could be causing this problem? Is it likely to be the sludge or will the problem still persist?

Your ideas would be most welcome as it is cold here!!!!!

 

[croydoncorgi]

It's not the sludge in the rads you should worry about. It's sludge FROM the rads that get into the boiler and causes blockages in the narrow parts of the heat exchanger.

In your boiler (if WB 24i is the correct type), the hot water and heating parts of the boiler are almost entirely separate, so sludge from the rads cannot have any effect on hot water performance.

Flushing your radiators won't do any harm, especially if they pre-date the boiler and were not cleaned when it was installed but there must be a different problem affecting the hot water.

When it cuts out, does the boiler show any fault indications (such as flashing mains light)? Do you need to do anything else apart from waiting and then switching it off and on again?

 

[queenb]

Thanks for the answer. The boiler is defintiely a Worcester 24i.
When it cuts out there is alight flashing on the front that we understand means a sensor fault, but the thermistors have been changed, so we don't know why it is flashing. This was confusing the engineer who looked at it, and was the reason he then changed the PCB board.
All we have to do to make it start again is turn it off and on at the mains, but it cuts out again within 1- 2 minutes- I timed it!!!!

Must admit I couldn't understand how sludge in the rads could suddenly overnight build up to a level that would cause all these problems!

 

[croydoncorgi]

AFAIR, flashing mains LED indicates sensor problem (only).

 

[queenb]

So any ideas what the problem could be with the sensor? And which sensor? What do we need to do with it??

The guy that came out to look at it was here over 2 days and still couldn't figure it out or fix it.

We could really do without having to fork out £200 for having the rads flushed if we don't really need to at the moment coswe don't really have it. But that was the only other explanation they could give.

 

[croydoncorgi]

The error condition either means the boiler PCB is not connected to the sensor at all (wiring problem), or the resistance of the sensor is 'all wrong' OR inconsistent with values of other sensors.

The standard method of checking is to take another known-good sensor and connect it electrically WITHOUT attaching it to the heat source. If the boiler then runs and CH / HW (whichever sensor) gets hotter and hotter, the PCB, wiring and sensor are OK. If you've still got the fault, it's the 'inconsistency' problem. Takes 5 minutes to get this far.