OLD Boiler

[the unheard]

Hi

I have a old Thorn Olympic 38/50B boiler which only gets my radiators warm. It would appear that the pump stops when the radiators are look warm, even if I set the boiler thermostat to max and the room thermostat to max. When I operated the pump directly from a separate 240 volt supply the pump runs all the time and the radiators become red hot as they should. Is there a sensor controlling the pump operation?

Thank you for any help given

 

[oldbutnotdead]

Are there any motorised valves on the system- unlikely from your description but worth checking.
First thing is check the thermostat, wouldn't be the first time the external knob wasn't moving the innards. If it is ok mechanically then check it electrically (isolate first of course before removing any covers)

 

[the unheard]

Thank you for your quick reply. There are no motorised Valves, just a Honeywell 3 port diverter valve. The thermostat is working, I can stop and start the boiler by rotating the temperature setting on the control.

 

[Harry Bloomfield]

It reads as if the 3-port valve actuator is temperature sensitive, opening its microswitches which call for the pump and boiler to run as the pipework warms up. What happens if you remove you let it set itself up to heating, then lift the actuator head off the valve, without moving the valve spindle?

 

[oldbutnotdead]

Hah. What do you suppose operates the 3 port valve?
Is that the room stat that switches the boiler on/off? If yes then think @Harry Bloomfield is on the right track with his microswitch theory or may even be a heat sensitive airgap in the (now very old) wiring

 

[the unheard]

Thank you guys for the suggestions. I will try removing the 3 port valve micro switch assembly, but I can't see the micro switches been temperature sensitive, they have no means of detecting temperature, I think they just control the limit of the valve rotation, stopping the valve motor at the end of it's travel. As far as I have read the three port valve operation is controlled by the HW/ CH+HW switch on the boiler, according to honeywell the valve will move to close the CH branch and divert the boiler output to hot water in the HW switched position. In the CH+HW position the valve moves to the centre position allowing the boiler output to feed both heating and hot water. Heat sensitive airgap in the (now very old) wiring, interesting theory! Definitely worth checking the wiring.

I thank you guys for the though you have put in to solve my problem. I will certainly give them a try

 

[Harry Bloomfield]

The microswitches, apart from controlling the limit of the valve motion, also trigger the boiler and the pump. The actuator is not designed to detect temperature, the cylinder and room stats are supposed to do that, but I am suggesting is it has maybe developed a temperature related issue. They do get quite hot in service, from both the heat from the pipes and the heat from the motor. It is also an easy diagnostic step to carry out.

 

[the unheard]

Thank you Harry. As someone who has a limited knowledge of heating systems I very much appreciate you advice. I did not realise the micro switches did more than limit the motor travel. But after your explanation, it makes sense, if you switch to H/W only you don't need the pump running. Can I take up some more of you time and run another theory past you. Since I managed to increase the heating system temperature by running the pump directly from the mains, my radiators are reaching a much higher temperature. As you will

 

[the unheard]

As you will Know, to clear an airlock/blockage the boiler thermostat is removed, the excessive temperature of the water clears the blockage. Do you think this could be the case. My house has a micro bore system, unfortunately the plumber who installed the system was not to bothered about nice bends, from what I have seen there are quite a few flat bends in the system. I can't face removing all the flooring or chasing the walls to rectify the problem.
I will still remove the micro switch assembly as you suggested and see if solves the problem.

Thanks again
Dave

 

[Harry Bloomfield]

As you will Know, to clear an airlock/blockage the boiler thermostat is removed, the excessive temperature of the water clears the blockage. Do you think this could be the case. My house has a micro bore system, unfortunately the plumber who installed the system was not to bothered about nice bends, from what I have seen there are quite a few flat bends in the system. I can't face removing all the flooring or chasing the walls to rectify the problem.
I will still remove the micro switch assembly as you suggested and see if solves the problem.

Thanks again
Dave

Must admit I have never heard of removing the boiler stat for any purpose and I would expect doing that to cause the boiler to overheat if you did. I don't really understand how you can have a blockage, if your trick with the pump got proper heat to the radiators.

I didn't suggest removing the microswitches, just take the actuator head off the top of the valve once the valve has been set to provide heating and before the actuator heats up. Usually it means removing two screws/bolts holding actuator head, to the valve. It is just a quick simple check to help you locate the cause of the issue.

The most troublesome part of a heating system by far in my experience, is the 3-port actuator. They jam, the microswitches fail, the motors fail.

 

[jeff the gasman]

Jeez! It’s more than likely the actuator head needs replacing assuming HW off and HW satisfied is working at the programmer and cylinder stat respectively.
If you select heating only does the system operate?

 

[MeldrewsMate]

Listen to @jeff the gasman.
Sometimes the motor driving the 3-port valve from 'shared' load to 'heating only' goes weak, the effect is that once the hot water cylinder is hot the system goes off, waiting for the valve to reach its end-stop (and operate the end-stop micro switch). Under normal circumstances it would do this in a few seconds, with a weak motor it may never get there!

Do you have a flow limiting valve on the return from the hot water cylinder? Without this ,and with a microbore system, flow will be preferentially diverted to the cylinder when the valve is in its mid position (shared load position), thus causing your rads to run cooler.

 

[the unheard]

Thanks for everyone's help. I tested the 3-port valve micro switch, it all checked out, resistor values,diode and micro switch operation. But just to make sure I changed the micro switch assembly. Unfortunately this did not solve the problem, radiators heated to Luke warm then the pump switch off. Unfortunately it is not possible to select heating only, the only options are "hot water/boiler off/heating and hot water". When switching between hot water and heating and the motor rotates to select the correct port. The motor is working as it was rotating while I was changing the micro switch. I'm very interested in the "shared load position" theory, I have looked for a flow limiting valve, but can't see one, unless it's under the floor. When the valve is in the "shared load position" is the power to the pump shut off?
As I said in my previous post, after seeing the flat pipe bends I don't have a lot of faith in the plumber that installed my system, maybe he did not fit a flow limiting valve. As suggested I'm going to remove the motor, put the valve in the heating position, operate the micro switch while measuring the voltage at the pump, I assume this will confirm if the micro switch supplies the pump power.

Chatting with you guys has made a lot of thing clearer

Thank you
Dave

 

[the unheard]

As I said in my last E-mail I have removed the 3-Port motor, then activated the micro switches in both closed and open positions, this did not operate the pump. which suggests, together with my multi meter testing of the switches this is not the problem. I have been doing further research on the net and came across this site https://www.flameport.com/electric/central_heating/heating_wiring_Y_plan.cs4. What an amazing site, fantastic graphics. According to this guy, the pump is switched on and off by the boiler, but it's not clear to me how this is done. I'm going to try and find where the pump gets it supply, but since the pump is up stairs and the boiler is in the kitchen it will not be easy to check for continuity.

 

[Harry Bloomfield]

According to this guy, the pump is switched on and off by the boiler, but it's not clear to me how this is done. I'm going to try and find where the pump gets it supply, but since the pump is up stairs and the boiler is in the kitchen it will not be easy to check for continuity.

Older systems had the boiler and pump switched by the actuators micro-switches, both in parallel, both ran simultaneously.

More recently, they changed this to letting the boiler itself control the pump - that allowed the pump to be run after the boiler had switched off, to remove residual heat from the boiler. The pump runs-on for a couple of minutes, after the boiler has shut down.

He has quite recently modified that diagram to reflect that fact. On older systems, what is marked as PL, would simply be connected to the one marked SL. There is another website which discusses at length the problems of unreliability of three port actuators.