DIY Doctor UK DIY Forums

Good afternoon everyone, I am hoping you may be able to help me. I have a Worcester Bosch 19/24CBI boiler and it keeps cycling. When trying to heat the hot water (same for heating) the boiler is off more than it is on and thus unless timed for a very long time never gets the desired outcome. In essence it was on with the burner lit for around 18 minutes in an hour and no burner lit for 42 minutes in an hour. Whilst the burner was off, the fan and pump remained running. The pump is quite new and I am sure has good flow. Below is the timings of the on and off cycling of the boiler covering an hour for info:
On 4:41
Off 5:57
On 2:47
Off 4:48
On 1:46
Off 5:14
On 2:10
Off 5:59
On 2:07
Off 6:46
On 2:18
Off 9:07
On 2:17

From time to time - every few weeks it also locks out and I need to reset it by turning the dial to the left and back again.

Does anybody have any idea what may be causing this cycling issue or locking out please? All ideas and theories appreciated as it’s an old boiler and I do not have a lot of money to throw at it.

I would assume an oil boiler? My oil boiler also works on a mark/space ratio, gas boiler are normally condensing which means they gain the latent heat, to do this they need to modulate, which means turn down the output, so the boiler output adjusts to demand, and is in the main controlled by TRV's on every radiator.

But oil does not tend to be condensing so it simple switches on/off.

It can still use TRV's to control room temperature and in the main pump is on supply and there is a by-pass valve so when the TRV's close the water by-passes the radiators.

However my boiler the pumps are on the return and I seem to have a problem with hot water returning which will turn boiler off, but radiators no where near as warm as the return water, so some where I have some by-pass and not a clue where it is.

Maybe you have same problem.

As to cutting out, again has the same, I employed a oil heating guy, and he tried many things until cured, crediting me with the cost of items found not to be faulty, which is likely better than trying to DIY where you can't return items found not to be faulty, with intermittent faults some times no option but trial and error method.

Hi JPM. I hope that you have solved your problem since your post is 3 months old.
Clearly Eric is mistaken about it being an oil boiler.

I think that it's because the water temperature thermostat is switching the gas off if the water inside the heat exchanger gets too hot.

So this could possibly be because the water isn't flowing fast enough. Maybe your CH system needs flushing.
Mike.

mdgibbs wrote:Hi JPM. I hope that you have solved your problem since your post is 3 months old.
Clearly Eric is mistaken about it being an oil boiler.

I think that it's because the water temperature thermostat is switching the gas off if the water inside the heat exchanger gets too hot.

So this could possibly be because the water isn't flowing fast enough. Maybe your CH system needs flushing.
Mike.

Thanks ever so much for your reply Mike.
I tried changing the overheat thermostat to no avail.
In the end I was worried to go through a winter with this boiler so replaced it with a Viessmann Vitodens 100-W heat only boiler. The problem has gone away and I have noticed it is a bit more efficient already.
Thanks again.
Jeremy