Alpha cb28x...Heating question.

[stevemcn]

Can anyone please tell me why my boiler turns off & then on again all the time, does not happen when hot tap is running..Rads are hot but would be constantly hot if the thing stayed on.I have had a number of problems & have changed nearly every part so now am running out of ideas. Have left messages for an Alpha tech to call back but I fear I`ll be too old & deaf by the time they get of their sorry arses & reply.
Cheers folks.

 

[gas4you]

What time span is it between the on/off cycle?

Is it there all the time, even at start up with a cold system?

 

[stevemcn]

Hi Dave, sorry for delay.

The answer to your question is yes, the boiler heats up rads, goes off then turns on again a few minutes later, the boiler runs for a few minute before turning off. It does it from cold as well. Dave, I have had alot of trouble with this thing. I have changed most of the parts in the boiler so now am thinking it to be an easy solution...... The hot water side of things are ok.

Cheers
Steve

 

[gas4you]

What parts have you changed?

Have the min and max burner pressures been set/checked?

 

[stevemcn]

Hi Dave,
I have had a new diverter valve assembly, manifold assembly had to be replaced as the part that connects the two together would not budge, two thirmisters,DHW switch.
I have checked room stat, this is ok & working. A guy from Alpha said to disconnect clock, did this, no change, he said if that doesn`t work to change pcb. I told him I`d rather get a new boiler than replace pcb as I have had nothing but trouble with this thing since day one, this is what you might call a Friday afternoon job. I have not checked min/max on the burner though, I would have assumed that was ok as hot water ok....but am willing to give it a go, is it easy to do?
Cheers Dave thanks for your time.

 

[DP]

Have you checked the temperature drop across the radiators? If the HW side is functioning correctly, that suggests the primary side to be in order as well.

For CH water leaves the boiler, flows through the rad and returns to boiler to be reheated. If flow is slow, sensors will modulate the burner. If flow is slower still, burner will go from high flame to no flame.

During HW demand, water circulates in the boiler. This it does without a hitch, so I would assume boiler itself is in not faulty.

Have you checked the connections to the boiler? Last time I looked at this boiler, I had to dismantle most of it to replace O rings and 'decoke' diverter and other parts.

 

[stevemcn]

Have not had too much time on my hands today but did check temp on flow & return. Flow pipe very hot, return not so. It would appear that water gets very hot but because it turns off after about 2 minutes it does not get round the whole system before shutting down.

 

[DP]

Boiler has to switch off else the water would turn to steam. Problem lies beyond the boiler i.e. to the rads. Circulation is poor. I would be looking for blockages.

 

[stevemcn]

Do I assume the blockage would be in the flow & return pipes. If I shut off all rads & flush the system do you think this might work. I was wondering what I might do today, now I know. Thanks DP, let you know what happens.

 

[stevemcn]

First of all I turned off all rads, connected a hose to the drain off & whilst draining system I kept a flow of mains water going through the pipes. Just clear water came out. I then started opening the rads one by one, still only clear water coming out. I wondered if I might be able to run the pump whilst draining just to give it a boost & dislodge anything that may be causing an obstruction, still only clear water coming out. Filled system, bled rads, turned boiler back on.... the same thing happens.
I was wondering whether the blockage maybe on the return ?
I am giong to give it one more go in a minute.

 

[gas4you]

Did you make sure that you closed the appropriate ch isolating valve under the boiler?

eg if the drain cock is on a return pipe, you have to close the return ch isolator so the fresh water is pushed around the circuit and rad rather than just straight down the return, thereby all you will get out of the hose is the clean mains water you are letting in.

Turning off the isolators on these may cause the valves to drip afterwards

 

[stevemcn]

Thanks Dave, I`ll give that a go once I have found the return ch isolator.