Boiler short cycling

oldskoo1

Just wondered what your view on the following is.

When I moved in I discovered the heating was poor and found the flow and return pipes coming out of the boiler the wrong way round. This means the pump was fitted to the return and effectively sucking water around the closed system.

I don't know whether this has caused any damage to the boiler or wider system.

I spotted this piping error and the gas engineer fixed it. I now assume the pump is on the correct flow pipe with arrow point upwards which should be correct. However if it was like this for 10 years is it possible the pump is damaged in some way.

I'm certain I hear bits of metal which have been attracted to the pump. The system is now 12 years old and I have isolation gates either side of the pump and a big pair of grippers. However I don't want to spend £120 on a new pump if it isn't needed.

I just wondered what potentially could have happened if it ran on the return for such a long time.

oldskoo1

Took the pump off

Checked the impeller and it turns freely, a little bit of blackening around the joins and centre screw. No real debris although a visual check insider shining a light into the outlet showed up the odd tiny bit of grit.

Back on and it's lasting 15mins before its first cut off then it cycles every 2 mins.

Flow is at temperature, return is perhaps half that. But finger touch is no real measure.

I'm just wondering if the burners are giving out too much heat that the return water can't cool it quick enough or wether there simple is a flow restriction somewhere.

Cardew

oldskoo1 wrote: »

Thanks guys

I don't think I can turn down the boiler output on this model. I read the manual and there is no way to do it. If I turn the stat down it just starts cycling much sooner.

Are we at cross-purposes here?


By 'turning down the boiler output' Pincer(post #9) presumably means the water temperature.


http://idealboilers.com/installer/wp-content/uploads/sites/2/2013/08/157019-2.pdf

Control of water temperature




1. Adjust the boiler thermostat (B) to give the required
temperature of central heating.




2. The boiler thermostat automatically switches the main burner


OFF and ON to maintain the selected temperature.


Approximate flow temperatures for the boiler thermostat settings


are:


Knob Setting Flow Temperature


°C °F






1 56 133


2 61 142


3 66 152


4 72 161


5 77 170


6 82 180

Could it be a simple case of a faulty water temperature sensor

oldskoo1

Isn't the limit stat on the flow pipe?

This is getting very hot it's the return that is cool

matelodave

If warm water doesn't return to the boiler then water isn't circulating in the system and the boiler will get hot and the thermostat will turn it off - have you got any motorised valves in the system as it sounds like there's something stopping water circulation.

There's nothing wrong with having the pump in the return leg, all it does is circulate the water so it makes no difference whether its on the hot or cold side of the boiler.

As an aside - my brother has had a similar problem with his hot water system.
A quick look at the diverter valve established that the motor unit was operating but the valve itself did not seem to be operating as it only got hot on the heating side when the boiler & pump were running.
A quick check by taking the motor off and trying to turn the valve with a spanner showed that it had jammed in the heating position. The motor/valve drive dog had stripped but was allowing the motor to operate as normal.
A new valve body & motor has cured the problem.

Surprisingly this had been checked by a plumber who couldn't find the fault as all he'd done is to check that the motor was operating. So try applying a bit of logic to the problem, feel the piping to establish where it's hot and where it's not and then try to find out why it's not circulating properly

oldskoo1

i think the problem before was the pump on the return was drawing water away from the boiler (upwards) and not pushing it back into the boiler. This was at conflict with the limit stat which was on the correct flow side. But in our configuration the flow was actually on the return pipe. That is now sorted. The easy fix would have been to swap the pump around.

We do get warm water returning but its probably half as hot as the flow when the boiler first cuts out. However eventually, the return does get within 10-20 centigrade (lower) than the flow.

I have a clip thermometer coming shortly so i can measure within a reasonable degree of accuracy exactly what the flow and return actually is.

oldskoo1

I had a go at taking the temps

Flow was 52c
Return 39c

Radiator same as flow
Pump 60c

Boiler stat roughly 66c (setting 3 of 6). I don't want to turn this up so kids don't burn themselves.

Not sure why the pump was hotter, maybe normal. Put black PVC tape on the pipes to get the measurement. It was consistently 10c - 13c lower on the return side.

Just wondering why my pump still makes a trickling sound. Also trying to work out if my pump is on the right way. I'm assuming from my pic the boiler flow water is flowing upwards into the pump and out through the grey valve into the CH circuit and that it isn't the other way round as both pipes get hot first and the pump arrow is point upwards on the pipe closest.



Boiler output is 23.4 kW
Flow required 30.3 l/min
Pump grundfos 15-60 on speed 2.