strange heating problems

[doozer]

Hi,

I really hope you can help me because this problem is driving me nuts! There is something wrong with our heating system which is causing it to just do random things. Sometimes it won't turn on and other times it won't turn off (this morning is a prime example of that). At other times it will come on maybe for a few minutes and that just turn itself off.

I come to you in desperation. There is such a shortage of plumbers in this area that they won't come out unless I can reproduce the fault while they are here but the fault is random happening for maybe a day a week. I did manage to talk to one plumber who thought it might be the circuit board in the boiler (the boiler is a Glow Worm Space Saver 50 MkII and looks quiet old) but I am really sceptical.

Anyway a few more details. The most dangerous thing that happens, IMHO (please excuse the fact I don't know what all the various bits are called), is when the boiler fires up but the hot water produced is not pumped around the hot water tank or the radiators (the pump goes ten to the dozen and sounds like it's trying to tear itself off the pipe). I am fairly sure there must be a safety cut off because under those circumstances the boiler does go off briefly. The Honeywell controller / timer box, an ST6400C

has been bodged on to the wall (previous owners fault) and tapping it, even very lightly, with my finger can cause the heating or hot water to come on.

If I had to make a guess I would say that it is the controller / timer box but I don't know for sure. Any ideas?

Bearing in mind our boiler is quite old I would also be interested to know how if you think it might be worth ripping it our and sticking in an instant heat system (or heat on demand)? At some point the house has had a loft conversion so it has no header tank - it has some complicated Megaflow thing-m-bob with a little red pressure tank instead. Removing the hot water tank would give us a lot more storage space so it is an option if repairing the existing system is going to be very expensive. Many thanks for getting this far down my rambling post :o)

[Markus Splenius]

Sounds like an electrical fault to me. Have you checked the wiring inside the controller box? Perhaps just the tightening of a screw would solve the problem.

Many people here find unvented systems like the Megaflow highly dersirable and wouldn't want to rip it out as it provides mains pressure hot water at a decent flow rate. (If it doesn't then you probably have a low quality water main!).

M.

[john]

I have a Glowworm Mk I. If the pump is going too fast, it suggest a lack of water in it which could be very dangerous for the boiler and persons standing too close. The boiler water can't be totally drained in mine as the feed pipes are at the top and half way down, so in the absence of a water supply, the burner will heat up what water is left in the boiler, until the boiler thermostat switches the gas off, which on mine would take one minute or so.

this is just a worst case scenario....... check the pipes to the boiler for temperature. If they are cold, they may have no water in them.

[Set Square]

It sounds to me as if the pump is cavitating through lack of water. Presumably the little red pressure tank is the expansion tank for the primary circuit (the water which flows from the boiler, through the radiators and through the heating coil in the hot water cylinder)? If so, there should be a filling loop for adding water, and a pressure gauge. Is there? If so, what does the pressure gauge read (a) when the system is cold and (b) when everything is hot?

Whatever you do, *don't* get rid of your stored hot water system!

[Ed Sirett]

Educated guess: You have a system with a small open header tank (almost certainly). Either the float valve has scaled up so that no water enters the tank or the pipe from that tank has blocked (just where it joins the main primary circuit). There is now insufficient water in the circuit, the pump is intermittently going dry (hence the noises) and all the other symptoms.

If you bleed an upstairs rad with the system off you will likely get nothing out.

[Ed Sirett]

Sorry I did not read to the end of your post.

The system needing topping up see the FAQ below!