Kitchen Garden Forum

Something very strange is going on. For the last week, every morning I went to my heated greenhouse only to find the window wide open and the heating on full blast. The fan heater is thermostatically controlled. Yesterday I changed the automatic opener for a different one as I assumed the old one had some fault. It was closed down when I fitted it at 6.30pm and as it had previously been set for use in my other greenhouse I didn't adjust it. I've just been out and found the window wide open again and it's been snowing and everything outside is frozen. The fan heater has coped and kept the temperature up to 12 but why is this happening? I thought it worked on air pressure and not heat? I've shut the window by screwing the vent right down and I'll have another look later, but this is getting silly. I'm going to have fuel bills bigger than the national debt!

Any ideas anyone?

most auto vents uce a telescopic cylinder containing a fluid or gas which expands as it gets hotter pushing the rod out to open the vent. they cannot open unless they get hot. if the cylinder leaks they just dont open. so its likely that the heater is the problem either the thermostat has stuck in the on position or something has knocked the controls.

The heater is on and off all the time and according to the min/max thermometer we're no higher than 20 and no less than 12 between 7pm and 6am. However, I'll reset the thermometer and the auto vent and try again tonight.

Thanks

I turned the heater to a lower setting and screwed the window shut at 60 yesterday evening. I checked at 2am and the window was wide open, the heater was on and the temperature was 62. The highest it had been was 70 and the lowest 15. Does this indicate my thermostat is definately knackered? I screwed the window shut and this morning it was still shut with the heater running but it wasn't too warm in there, still a max of 70. Should I just cut my losses and buy another heater before I kill everything? However, the problem with this idea is that nowhere has fan heaters in now (I checked yesterday at my local garden centre, hardware shop, Tesco, Sainsbury and Homebase, as they're "out of season" for pity's sake. There is a huge but very expensive garden centre outside of town which will probably stock them but as a pair of gloves from there costs £10.99 and the same pair is available in Wilkinsons for £2.99 I shudder to think of the cost of a fan heater!

Have you got an old fashioned electrical shop anywhere near? I bought my new one from one of these this year and they were cheaper than any of the big DIY places.

Hello,
If your system has worked fine previously then it may be your heater that has gone wobbly..

But are you sure you have not got 2 systems that are fighting one another.??

Cold on floor of greenhouse where the heater and its thermostat may be sited.??...heater comes on.. heat rises...auto vent "thinks" things are warming up here and opens...Heat legs it out of the window...heater "thinks" blooming 'eck not doing much good here must keep £-ing in supplying more heat which continues rising and escaping...

All the best,
Clive.

Chantal, where abouts in relation to the vent cylinder are you reading your greenhouse temperature. I think if you attached a max min thermometer actually too the vent operating cylinder you might get a better picture of what is happening. But I think its just one of Sods laws that says hot air rises cold air sinks causing the vent to open and the heater to come on.

Instead of replacing your thermostically controlled heater buy a rodstat and use it to power a socket then just leave your knackered heater at maximum. Rodstats are more sensitive (on / off closer together) than built in stats. You can get some that can be used both ways - off as temperature rises or on as temperature rises - so you can use them to control a fan in the summer.

I've never heard of a rodstat Geoff, I'll investigate that option.

Re the other questions, firstly I don't have anything low down plantwise in this greenhouse, it's all pots and compost beneath bench level etc so the heater is in fact at about 3.5ft up on the bench near the door. The thermometer is at the same level hanging on one of the window bolts but not in line with the heater.

I'll move the heater to nearer the floor and the thermometer to up by the vent as suggested and see what happens tonight.

Cheers

I knew all that helpful advice would confuse the old girl.

Kind regards the cheeky Old Herbaceous.

To many cooks spoil the broth.

Just a bit, but the heater is now 6 inches off the floor and the thermometer is up by the vent. I'll report in tomorrow...

Thanks for all your help guys, maybe it was just the positioning although why this should suddenly happen after 5 years I don't know! The max temp was 62 the min was 15 the window appeared to have stayed shut. All my babies are fine and I am very relieved.

Thanks again

Here is one example

http://www.twowests.co.uk/TwoWestsSite/product/THPR.htm

There should be better sources, this seems expensive, I'll do another search when I have chance.

Chantal when you see the postman struggling up your garden path you will know he or she has got your electric bill.

Kind regards a very jovial Old Herbaceous.

We will always get some sort of weather.

That is worrying me just a bit OH. Oh well, I sort it out somehow, and thanks for the info Geoff.