HELP! my hot water heats but central heating does not?

[Devonman666]

i have a central heating system, wall mounted gas boiler downstairs, hot water tank upstairs and header tanks in the roof.
the heating system has two honywell motorized valves, two port that both look a little old.one valve for hot water and one for central heating The hot water heats fine, boiler & pump kicks in when required. the central heating however will now not work on its own, it has been doing so until 2 days ago. if i run hot water out of the hot tank the boiler & pump will start and run ok, the hot water motorized valve opens but at the same time the rads will heat up. when the hot water in the tank is back up to tempature everything stops but the central heating motorized valve is still open but pump does not work. the central heating motorised valve is definitly working and opening, water would not circulate around the rads otherwise. when i turn the room thermostate off the central heating motorized valve closes, turn the thermostate up the valve opens. when i turn the heating off on the electronic timer the valve closes, turn it back on and the valve re-opens. the pump is a Grunfoss and this is working fine with the hot water. it is on the fastest pump setting and runs very quietly. i can only deduce that either the central heating motorised valve or the electronic timer unit is not sending a "message" for the pump to run or the boiler to fire.
can anyone help please

 

[seco services]

More likely the micro switch is faulty that is activated in the valve actuator when the valve opens.

 

[BlueMoonMole]

You have done very well fault finding so far, most people give up at the clock...

You're on the right lines...

You select Heating ON and 240vac is sent to your Room Stat.
Your Room Stat requires heat and sends 240vac to your CH 2Port.
The valve recieves power and a synchron motor inside spins...

This will also motor the valve open and finally hit a microswitch which will send power to your pump and boiler...

Et voila! You need to isolate the power and remove the cover of the valve, check if the arm requires adjusting, the synchron motor replacing or the whole valve replacing.

A synchron motor service kit is relatively cheap.p

 

[Devonman666]

More likely the micro switch is faulty that is activated in the valve actuator when the valve opens.

many thanks
i am guessing the micro switch is part of the motorised valve unit? i think i can buy a new motor unit (less valve)and replace? (i have travelled back from Colchester today. is it still cold up there?)

 

[Devonman666]

You have done very well fault finding so far, most people give up at the clock...

You're on the right lines...

You select Heating ON and 240vac is sent to your Room Stat.
Your Room Stat requires heat and sends 240vac to your CH 2Port.
The valve recieves power and a synchron motor inside spins...

This will also motor the valve open and finally hit a microswitch which will send power to your pump and boiler...

Et voila! You need to isolate the power and remove the cover of the valve, check if the arm requires adjusting, the synchron motor replacing or the whole valve replacing.

A synchron motor service kit is relatively cheap.p

brilliant reply, most helpful. i think i will probably go for a new motor unit complete as the old one is very rusty and knackered looking at not sure if the return spring is 100 percent, covers a bit loose as well. i'l nip down the plumb centre in the morning ( i will go for the easy option and turn the electic off at the mains for the whole house when i do the job, that'l please the missus!)

 

[seco services]

It's still bl**dy cold tonight.

Yes the m/switch is part of the valve actuator.
Check your silver cover on the later models it has a pimple on the top of the cover the early ones don't and would need a kit to be able to change the actuator the new ones just lift off.

But as said remove cove and check it being hit when motor moves the valve across

 

[Devonman666]

a big huge thankyou to seco services & bluemoonmole for your fantastic assistance

i changed the motor head unit today and all now working perfectly. the lever that pushed against the micro switch on old unit seemed to be a long way off the switch. looks like the lever had seen better days. a fairly straight forward job to replace the unit, trickest bit was haveing 5 wires on the old unit & 6 on the new and working out the right ones.

biggest job is putting the front of the airing cupboard back together!

once again many thanks for your help, much appreciated

 

[The831Bunny]

You'll need to electrically isolate that sixth wire with tape or put it into a spare terminal in your wiring centre as it will be 240v live when the valve is shut. I'm assuming the valve is a Honeywell 28mm. They are usually 6 wire.