Hot Water but no Central Heating

[wackyraces]

Hi All

I tried to help a friend out today with his heating system. but failed. Basically the hot water on the system is working perfectly but the central heating is not. If you switch the whole power off to the heating system and then back on again, then switch the central heating on, the system powers up, pump goes and boiler fires up. After about 1 minute it goes off. The pump switches off and the boiler stops. The room thermostat is on to max temperature. The radiators are standard rads with no thermostats. If you switch the hot water on, it all fires up ok but does not heat the radiators. The boiler, is a Vulcan boiler. The switch unit is by Thorn Emi. I'm not sure of the model details.

Any help on the matter would be very much appreciated.

 

[boxster]

you know what i have never repaired or even seen a vulcan boiler, noone has them installed in my area, north east.. however i am guessing here maybe chris or someone might be able to help better. If the heating only comes on for one min and cuts off, check and make sure the heating is actully getting away from the boiler. If the pipes on the boiler are hot and rads are not make sure all rad valves are open.. make sure the boiler heating pipes are also open fully. other than than you may be looking at a blocked heat exchanger. maybe the stat is not working or a simple fault with the diverter valve
could even be air???

again i dont know what this boiler looks like... i thought i knew every boiler, maybe i need to check more of the older ones...

 

[wackyraces]

Thanks for the reply. The radiators do actually start to get slightly warm within the 1 minute it is on. We kept switching it on and off and so the radiators do heat up. I thought it might have been the thermostat on the boiler but if it was, I doubt the hot water would work.

 

[boxster]

the hot water would still work. i would say it could be the stat try changing it.... would you say your h/w is hot as in very hot or just normal. also it could be the diverter valve not swinging fully across only letter a small amount of heat out... try the stat first tho!

 

[wackyraces]

Thanks for the reply. The hot water gets very hot. I checked the diverter valve and that's moving across OK. It's a 3 position valve. It moves to the middle when both the hot water and heating are on. I thought it might have been that. I'll swap the stat out and try that. Thanks for the help.

 

[boxster]

ok mate i am sure its the stat tho best of luck

 

[ChrisR]

Bit surprised the rads don't get to a reasonable temp if the HW gets very hot. Slide the boiler stat sensor out of its tube inthe cast iron while you wait to see if the flow/rads get hotter - but don't leave it out!! Could be the 3 port, if it's leaking a lot to the HW when it's on CH.

Boxster I can assure you you've been into a lot more boilers than me - I've only been at this lark 5 minutes.

 

[boxster]

oh, well you seem to know what going on a boiler. i agree with you about the rads they should bet hotter but its hard to explain what the term HOT means. I had a wacky customers the other week she moaned on she was freezing when her old boiler packed in. We installed a 24i and now she is moaning she is too hot... the rads are not even as hot i want mine but she thinks there boiling.. and thats with her boiler stat on 1 lol

I think the problem with this job is the stat is faulty and simply not reading at all. the hot water would be very hot as the heating might have no where to go. I had the same problem with a vokera 80sp. the only way it would work is by re-setting the boiler so i flushed the heat exhanger out and it worked fine. Sometime if heat cant get away quick enough the boiler thinks its been on for ages. Also make sure the pump is spinning... put a screw driver to your ear and the other end on the pump, does it come on??

 

[wackyraces]

Thanks for the replies. The main pump switches on and powers up. The water starts to pump round. It then all stops and the boiler switches off. I tested the stat with a test meter and when the heating is on for that short period, there is a reading on the tester. As soon as it switches off, then there is no reading, even though the stat is on max. I shall check the things you mentioned and see if it is any of those. Thanks again.

 

[breezer]

what is "the reading"?

 

[wackyraces]

I just did a standard continuity test. This is the first time I have ventured into the depths of boilers and central heating systems, so I wasn't sure what to test for.

 

[ChrisR]

"As soon as it switches off, then there is no reading, even though the stat is on max. "

If by that you mean that the supply to the roomstat goes off, then it's your programmer that's faulty!!!! What is the make & model of the programmer and room stat? Tried it with CH permanently on?

 

[boxster]

MIGHT BE but i think its the boiler stat

 

[wackyraces]

I've tried it with the CH on permanent. The light comes on the programmer but nothing happens. If you switch all the power off to the central heating and then switch back. Put the CH on permanent, it powers up and the heating starts up. Pump starts, boiler kicks to life. After around 1 minute, it all stops. Boiler goes off, pump goes off but programmer light is on and switch is on permanent. Room stat is on max, so it will be continual. The programmer is an old Thorn EMI. I'm not sure of the model, as it doesn't say anything else on it. If you put the HW on to continual, it all fires back up, the pump switches on and the boiler starts. The radiators do not heat up though, only the hot water. Thanks for all the help.