Low pressure LED on Puma 80e

[Oddsocks]

Hi,
I have a Puma 80e that has been giving me intermittent problems for some time. Here's a short history of my boiler problem.
The system is about 8 years old and it has give me good service despite failing in the depths of winter. There's no evidence of Global warming in our house
The problem
After having the central heating on for about 12hrs constant the reading on the pressure gauge drops to about 1.0 bar so the Low Pressure LED comes on and H/W and C.H ceases. I re-pressurize the system, but that doesn't correct the fault and the LED stays on.
There is a tiny drip on the diverter valve, but hasn't affected the performance over the last 4/5 months.
This same problem occured in Oct 2004 so I studied the Installation & Service Manual fault chart and it stated that if the problem persisted after re-pressurizing, replace the Water Pressure switch with a new one. This I done; No joy
Thinking that it could be the Modulation Control Board giving a false reading I tapped the the PL-1 connector (top left of board) with an insulated driver and I saw a tiny spark behind one of its terminals, the Mains & Low Pressure LED's then went out. I removed the board and resoldered two cracked joints and replaced it. Still no hot water or heat
This same problem has happened in the past and has baffled a competent Central Heating engineer, but for some reason the system has righted itself a day or so later. The Low Press. LED has gone out and everything starts up. Plenty of H/W and C.H. works just fine.
I hope someone can help, I don't want to call in a plumber because I just cannot afford his charges. If anyone can suggest a quick fix to tide me over 'til spring I'd be really grateful. I can post a pic if requested
All help appreciated,
Tony

 

[BDL]

Sounds like the pipe to the water pressure switch is full of crud.
Remove the water pressure switch, get a small device (I normally use a small allen key) and push it into the hole where the pressure switch fits. You will probably find hard encrusted crud blocking it. Refit switch, refill should now be ok.

 

[weargas]

just an addendum to bdl's post, poke the "device" into the hole in the manifold as well as the switch.

 

[Oddsocks]

BDL & Weargas,
I gotta tell you lads that your advice worked a treat and I'm extremely grateful. The Water pressure switch and the manifold was gunged up with scale so I cleared them out and *WOW* Hot Water!
My wife reckons that the flow is much faster than before. Is that a good thing?
Do I have to bleed the pump, if so, does it have to be running?
Best wishes,
Tony

 

[Oddsocks]

Well fella's my elation is short lived, the Low pressure LED is back on and I have no H/W or C.H.
After I'd cleared the pressure switch and manifold of scale and re-fitted it, I tried the hot water and ran it for a short while, but I turned it off after a couple of seconds because I hadn't bled the pump (I have since). For the short period that the H/W was running a RED LED on the modulator board lit up. According to the fault chart that I have, the water flow switch should be changed, but brand new one was fitted 6 months ago.

I turned the Central Heating on and it fired up and ran OK. Every rad warmed up and it ran for about 15 minutes. To make sure there wasn't any leaks I popped my head in heating cupboard and was greeted by the dreaded RED LED. Boy! am I disappointed, I thought I'd cracked it when the system fired up. Alas, the problem is back and I don't know where to go from here.
All help appreciated
Tony

 

[BDL]

Remove the switch again, see if any more muck has got in the switch/manifold. If that is clear and the low pressure neon is still on then a new water pressure switch is needed. Have you got a multi meter?
If so check for continuity across the switch while the boiler is pressurised.

 

[Oddsocks]

BDL
Thanks for the prompt reply.
I will do as you say and clean out any residue in the switch/manifold.
I have checked the continuity of the switch with a digital multimeter (with the system pressurized and disconnected from the elec. supply) and I get a reading of 00.05 ohms, I don't know what that tells you. I would have thought it should have read 0000 as I get when I put it across a good 13 amp fuse. But I'm hanging onto your advice because up to now you're guidance has been spot on.

 

[BDL]

Email me and I will give you a definitive test to do. I cant post it on here because it involves a definate safety component on your boiler. (see my profile).

 

[croydoncorgi]

STOP!!!!
The RED LED on the PCB is ENTIRELY NORMAL when the boiler is doing hot water. It is completely unrelated to low pressure and is NOT a fault indication. It simply indicates that the DHW pressure switch has closed and is connected to the PCB!

 

[Oddsocks]

Have I discovered a further problem.
After disconnecting from elec and closing isolating valves, I removed the drain plug from the pump. The water drained off until an occasional drip, indicating the system was empty, so I loosened the pressure switch. The drip from the pump turned into a torrent and I got half as much water out again. Yesterday when I performed the same exercise ALL water drained completely through the pump before the pressure switch was cracked. So I'm hoping this only indicates I have now cleared the blockage between diverter valve and pressure switch.

BTW, the pressure switch has 0.5 stamped on the rim. Is this the continuity value when pressurized? Because when the same test is carried out on the switch when it's removed I get 00.00 reading across the terminals.
This will end up like 'Book at Bed Time'
Pass me the Prozac and a hot water bottle!!!!!
Thanks,
Tony

 

[kevplumb]

just out of interest whats the system pressure

 

[Oddsocks]

It is 1.0 Bar on the pressure gauge.
Last night I topped it up to 1.5 Bar and by this morning it had crept up to 2.3 But I have since drained the sysem off and refilled.

 

[IanDB]

I get a reading of 00.05 ohms, I don't know what that tells you. I would have thought it should have read 0000

0.05 ohms is 5/100 of an ohm in old money or to put it another way - a short circuit. Those 5/100's are just a bit of residual contact resistance plus probably a slightly bad connection between the meter at the contacts.

No problem with that reading at all.

the pressure switch has 0.5 stamped on the rim. Is this the continuity value when pressurized?

No. Nothing to do with it.

 

[kevplumb]

is it just me getting confused here
the origonal post was about dropping pressure

now you are saying its going up

 

[Oddsocks]

A little bit of confusion Kev. I asked for help because the Low System Pressure LED was lit up and the boiler was dead. No Hot Water and no Central Heating when called for.
When I cleared the scale out of the Water Pressure switch I got heat and H/W for a short period but the boiler died again. The Pressure Gauge was stable and the Low System Pressure LED was lit.
The messages I have posted are factual and I've tried to explain the problem as best as I can. I can't figure out the whims of a temperamental system.
I have just been across town to buy a Water Pressure switch and I left the system fully charged; electric on, all valves open, pressure gauge 1+.
I raced up stairs to replace the suspect Pressure switch and..... guess what! the Low Syst. Pres. LED was off. I switched the C.H. on and the boiler fired up again. But only for about ten minutes then it died.
It's as though something is tripping when a certain temp is reached.
Tony