HW but no CH - Central Heating Problem

3 Nov 2005
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United Kingdom
Hi all
I have a problem with my central heating system which was working fine up until yesterday. Hot water works fine but no central heating system. Boiler heats up hot water ok via an immersion tank , temperature controlled by a thermostat belt wrapped around the tank.

Central heating not firing up the boiler at all. We have an old Honeywell thermostat with a dial. You can hear a click sound when you turn it above/below say 15C.

The timer progammer is an old Satchwell Sunvic programmer/timer which i never got to work out how to set it. Until recently we always had it permenantly set to 'ON' for HW and CH, but when i saw the gas bill, i decided we would manually turn on the HW/CH as an when needed otherwise we found everytime we used HW, the boiler would go on to heat up the water in the tank which was not needed all the time, thats the way it works i suppose because used water is diplaced by cold water...
Anyway , we had been manually turning on the switch for HW and CH and then setting the desired temperature for CH on the thermostat.

Now, CH does not work....The LED lights come on ok on the HW/CH programmer/timer. and thermostat appears to sound ok when you turn the dial but cannot be sure. Boiler seems ok at HW is working ok
The boiler we have is an IDEAL E-Type.

Please could someone advise on what the problem could be....your help will be much appreciated

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Turn ch on
Find pump - it's probably stopped.
Try changing speeds on it and listening for action, it'll be obvious.
Else undo central screw and insert screwdriver to feel for spinning. (dribbles).

If the pump's as old as the boiler it's due a new one!
Thanks for the advice.

I put CH on and I tried changing speeds on the pump which is a GrandFos type usb15 (there were speeds 1, 2 and 3, and it was set to 3)..but no joy/

I started undoing the centre screw and water started seaping, so i have screwed it back in afraid water was going to gush out.... i have tried screwing the centre screw tight as i can and water is still dripping out from there, am seeing droplets of water falling down now, ive put a bucket under it.......it gets worse :cry:

help !!!!
in addition to above, pump is not making any noise whatsover when i change the speeds...

Q...will the boiler only fire up if pump works first ?
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This happened to mine a while back.

Turn CH and HW to off.

Remove the cente cover on the pump and stick a bowl under it (only a small amount of water will come out), put a screwdriver into the slot that you have just uncovered and try turning it. If it spins then your pump is knackered and needs replacing.

New pump costs about £20 if I remember correctly and is a doddle to fit. Just remember to turn off the electricity and water supplies before you go playing with it.

Also - use your old rubber seals, they'll be bedded in nicely and will reduce the chance of the new ones leaking!

I will give it a go and let you all know how i got on ...
We have tried the following :

1. Opened up the cover of the pump and inserted a screwdriver in and turned it...internal part of pump spins and stops...

2. We initially thought the pump was not working, but we opened up some of the HW taps in order to drain some of the HW in the immersion tank and force cold water to go in the tank , lowering the temp of the water and forcing the boiler to come on to heat the water ...When this occured we observed the pump was working. We found that when the HW is turned on and requires to be heated up, boiler comes on and pump operates .

3. We then turned on the CH, but nothing happened...therefore pump seems to operate for HW but not CH.

I am left a bit confused , not sure what it could be now, possibly the thermostat , dont know...
Santorium, you said if it spins then the pump is knackered. Do my findings still indicate a bad pump or do you think it something else?

ps , the reason wy water was leaking from the screw on the front of the pump because we found the washer behind the screw was gone and needed replacing..

any other suggestions anyone ???


Good evening Kushdy,from your recent posts,it seems that you have a fully pumped heating system.You have stated that your domestic hot water side of things is operating correctly.This implies that your boiler and pump are operating correctly.The system will therefore be operated by a three port motorised valve,or,two motorised zone valves,commonley termed a:Y PLAN: or S:pLAN.Both of these types of control system have a manual lever on the side of the valve ,which you can manually operate in the event of motor failure or stat failure.Doing this will ensure that you can have heating and hot water,until problem is solved.Sugest a web search on Honeywell valves.Hope this info is of use to you,Mike.
Gasman1015 & Mikeyboy ...Thanks for advice.

Directly vertically above the pump is a Honeywell unit attched to the pipe coming out of the pump , which i have searched around the websites and turns out to be what you mentioned , a motorized zone valve. On the bottom of it there is a small lever which is set to ' Auto' ..i have switched this to 'Manual'...i assume this follows the 'S' plan...

Switching to 'manual' does not seem to have started the CH off ....

Ill try again in the morning....


Very interesting post - I have exactly the same problem - HW no CH - the Y Plan valve (Honeywell 4073) seems to have given up and unfortunately I can't switch the manual level (completly stuck could be corroded?!?!). Although the boiler and pump are working fine when - when turning up the thermostat in the house - the boiler dosen't fire - is this simply because the water is hot enough and no ch (no diverter valve) means no need to heat up the rads?

Cheers Dave

Whatever house I have - always every November - heating goes wrong!!!!!! Maybe we should move somewhere hotter
Dear Lord - I tell a lie - through a little persuasion - I have managed to open to the valve to manual !!! And have answered my question - the ch is working for now - I'll get a replacement diverter and then my next decision - do I fit it myself!?!?!?!? Simply coming on this site has given me the inspiration....

How long can I leave the valve open to manual - would this cause any secondry problems if I left it open too long (i.e. a couple of weeks etc?)

Will not cause you any serious problems, you may be able to just change the motor, if you are confident.
Morning all, thanks for your continuing feedback

the plot continues...

last night i left the Honeywell valve set to Manuual , nothing happened at the time, but when i woke up and felt the rads, they obviously came on overnight....although they felt like they hade come on and had gone off, as they were warm from the top and alot coller down the bottom.....

I have turned up the thermostat this morning and switched the valve back to Auto, I am going to to see if it still fires up....if it doesnt then its definately the valve...

could someone explain the purpose of this valve connected to the pump?...infact there it like a T-connetion in the pipe coming out of the pump with another pipe branching out from it, im guessing the other pipe is HW , and the vertical part of the pipe where the valve is connected is CH.
I have also had a look near my immersion HW tank and there is another valve like this connected to the pipe there also, it does not have the Auto/Man switch on it..

pls check back later , ill let you all know my findings...currently seeing what happens if i turn of the thermostat and changed valve back to Auto....


Santorium said:
This happened to mine a while back.

New pump costs about £20 if I remember correctly and is a doddle to fit. Just remember to turn off the electricity and water supplies before you go playing with it.

Also - use your old rubber seals, they'll be bedded in nicely and will reduce the chance of the new ones leaking!

£20 ?!! I'll have a dozen of those please - try £50 for a Grundfos

Use the new seals and lubricate them with (ONLY) silcone grease, nut can then be hand tight + 1 flat to get good seal.
Note the orientation of the pump shaft meets manufacturer's requirements for long pump life.
Note the pumping direction, usually towards the 3 way valve.

Use the pump isolating valves, but don't rely on them to do a perfect seal, have a bowl/towels at the ready....

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