Central Heating intermittent fault

T

Tangoman

Well-Known Member
A friend has a combi boiler that was working fine until this winter when the downstairs rads stopped heating up. A plumber visited and played around with the valves on the upstairs rads, but left saying all good and she'd just need to play around with the valves some more.

I went round last night and I think there's a fault on the boiler too. With the thermostats fully open downstairs and all upstairs closed off, the boiler only runs for a period of time - not long enough to fully heat up the rads downstairs never mind the rooms.

Any thoughts?
 
Sorry - yes it's a Glow-worm Ultracom cxi

No fault codes - water heating works fine - just as I said, it doesn't run for long enough to heat the house properly

If I perform a reset on the boiler, then it kicks into life again.
 
Hi

To me it sounds like the problem is with the system not the boiler, or it maybe the pump ?

It may be the rads upstairs get hot with the help of gravity, and not enough power to get to downstairs rads.

To decide, you need to see how it was piped up.

Or the system downstairs is blocked with sludge


Regards
Peter
 
The downstairs heaters work, if all upstairs turned off, but only for a while - then the boiler shuts down as though it had nothing to do.

There is a magna coil on the system which I took apart to clean - it was pretty clear though - only a small handful of grit on it.
 
If the boiler runs fine when supplying the upstairs rads, I would hazard that the boiler works fine...

Did this plumber try tweaking the lockshields on the downstairs rads open a bit more? I think that's one of the first things I'd try - even if it's cvhust to one rad.

TRV fully open (and check that pin is moving freely) and crank open the lockshield an exact half-turn ('cos then it's easy to close it the same amount afterwards).

See if that rad heats up better.

It does sound as tho' the boiler is simply responding to a restricted flow - it can't disperse the heated water fast enough so shuts the burner down - so if this happens when the upstairs rads are closed down, it would suggest that possibly the downstairs rads are being restrictive too?

"A small handful of grit"?! What do you mean by a 'small handful', and what do you mean by 'grit'?

Perhaps add a good dose - perhaps double - of X800 in via that Magna filter and see if it then starts to collect more sludge. If it does, then you may have your answer.
 
Even when supplying just the upstairs, it seems to turn itself off rather sooner than I'd expect - one or two rads get up to full temp, but not all.
Basically there are 4 rads up and 2 down, and I'd say they fall into 3 cats - 2 up heat up quickly to hot, 2 up heat up slowly to almost hot, 2 down only heat up to warm if all upstairs switched off.
I opened all the lockshields full when checking the rads.

The stuff on the magnacoil was black and slightly gritty - probably about 3-4 tablespoons worth of the stuff - the water that came out was clear.
 
'Gritty' sounds unusual - I wonder if some of the pump's blades are breaking up?

If the boiler is still shutting down too quickly when the valves are open then I guess that narrows it down to things like a failing pump or a sticky diverter valve.
 
Forget gritty - it looked a little gritty although it was my friend who cleaned it - it probably wasn't actually gritty.
 
When the CH is running, does turning on a hot tap make the diverter valve 'click' crisply, do you know? (Not sure if it would be obvious anyway...).

Or, does the boiler seem to react cleanly to having a hot tap turned on and offski with the CH on?

Anyhoo, since the owner has a Magnaclean fitted, I'd be tempted to add a dose of X800 in there and monitor the sludge collected. If the issue is down to a partial pipe blockage (which is quite possible) then this should hopefully indicate it by improving the situation.

In which case add a further dose... :)
 
Ok 1st ignore the plumber that visited he's useless.

Are the radiators getting hot? Check both the pipes on any radiator, what ones the hottest? Is the rad that hot? Have you circulation through the rads?

The boiler will run at low gas rate if it can disperse the flow from the boiler or the return temp is up to temp.

I'm guessing your TRV's are stuck, remove a TRV head and push in the pin a few times
 
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