Why is my CH so rubbish? (Potterton Puma 100e Combi Boiler)

[Nige F]

Here's the best bit!

In response to the last reply, the plumber who came here was in his mid to late 40's. (are there lots of elderly plumbers out there?!!!)

Sadly we're in Leicestershire so your kind offer won't work out!

Oddly, I went to a local post office and got chatting with the post lady, it turns out she lived in our house as a child and left in 1971. She said there was no central heating then. Would we therefore still have a single pipe system do you think?

No, that`s when I started and we were putting 2 pipe circuits to rads .. but Gravity Circuit to Hot water cylinder. Sounds like you`ve just got a Pain In The Ass System

 

[baxpoti]

I'd be looking for a tired pump.

 

[ChrisR]

I'd be looking for a tired pump.

So would I!
Most pumas are of an age now where the pumps are getting a bit clogged/worn/slow.
Would also be checking whether the diverter valve is letting the water whizz round the hot water loop leaving no pressure for the rad system.

If you want to check for sludge, take a small (to be easy) rad off and see what colour water comes out. Flush it with a hose in the garden. If you just get a llittle black stuff at the bottom, forget about it until you change the boiler.

I haven't seen a Puma yet which HAD to be changed. They need new parts fairly often but seem to keep going. They're fairly easy to work on and all the parts are available. If you're unlucky and all the bits fail together, then fair enough, but I've not seen more than 3 (big parts) go at once!

 

[bab]

went to an 4yr old combi some years ago that had.nt been touched since been added to an older system. No inhibiter so no likley flush when fitted & it was same symptoms as yours. fitted new pump head & no better. stripped boiler to find 80% scale/sludge blockage in flowpipe just before boiler service isolater. Glass pipework would make our job easy.

 

[Agile]

If the boiler is firing on CH then the heat has to be going somewhere!

Are you sure its firing constantly and that a tap is not dripping or the diverter valve failed???

Tony

 

[ChrisR]

Anything can block up!

 

[adamtw]

The boiler fires up on the CH then after a few seconds goes out again.

Last night was another total weird one. Left the CH on all night, I woke at 4am to find the rads all warm (not hot despite it having been on since 5am the previous day), by 8am they were all stone cold and the house was freezing again. I just do not understand what the hell is going on. I'm at my wits end.

As I have said before, I'm not a plumber and I have NO idea if the diverter valve is working as it should be or not, I don't even know where it is. No offence to anyone on here and all those who have offered advice, but when you're not a plumber like me, it's a scary task inviting plumbers in to look at it. As we can see from this thread alone, there are so many different opinions, I could spend hundreds trying different things and get nowhere.

One chap said before, had I tried shutting off the cold water to the boiler to see if it improved the heating.

Can someone please tell me why this might work, how long I should try it for, will it affect my HW while its off and what would this show if it did work?

I just spoke to the Baxi/Potterton service team, they want to charge £349 inc parts, labour and VAT to fix any/all problems and give me a 1 year warranty on the boiler. If the flushing does not work, this might be the next step, however, then I have to wonder if we may as well start looking at a replacement boiler completely than spend money on this old thing.

Any thoughts? As a general rule, what percentage of the boiler cost is added by installation etc? Another 50% 100%?

Thanks again everyone.

 

[Agile]

One chap said before, had I tried shutting off the cold water to the boiler to see if it improved the heating.

Can someone please tell me why this might work, how long I should try it for, will it affect my HW while its off and what would this show if it did work?

Either the pump is failing, a cold water flow keeping it in DHW mode or the divertwer valve failed.

You dont need to know how the boiler operates as we know that. In spite of what customers think, a competent boiler engineer is quite a clever person. I appreciate you cannot tell the difference between an ignorant plumber and a boiler engineer.

If you want to check its not a water leak then turn off the mains water to the house and turn on a hot tap and see if the heating comes on for 30 minutes.

If not then its either a failed diverter valve, my expectation, or a failing pump.

Tony

 

[adamtw]

Tony,

Is there any way in which to diagnose if it is the pump or the diverter valve without actually replacing them or is it a swap-out and see job?

Thanks

Adam

 

[Gasguru]

DO WHAT WE SAY AND GIVE US A CHANCE OF DIAGNOSING THE FAULT

Temporarily turn off the cold water feed to the boiler. Then run the heating for 10 minutes and see if it improves. The design of the diverter valve is flawed, the smallest drip from a hot tap or leak on the hot pipework will prevent the heating from working. In addition after 6 or 7 years the wax element in the front section becomes sluggish to operate.

If the heating still does not improve the chances are the diverter requires replacement (or at least the front end section). Most Puma's are now on their second diverter since they often start to play up after 6 or 7 years.

From completely cold switching on the heating will fire up the burner and the pump will run. After say 20 or 30 seconds the burner will extinguish but the pump will continue to circulate water around the boiler (in a loop). Gradually heat is conducted from the hot rear section to the cooler front section of the diverter valve. Once the front section is sufficiently hot the wax element inside operates imparting motive force to the rear section and allowing hot water to flow to the radiators. If the front section is unable to reach a sufficiently high temperature (say due to a dripping tap) the element will not operate the rear section.

 

[ChrisR]

Baxi/Potterton service team, they want to charge £349 inc parts, labour and VAT to fix any/all problems and give me a 1 year warranty

Bijaysus. For that I'd happily fit a new pump, diverter, pcb (it'll need one soon) and a couple of temp sensors. And they can still turn round and say it's your dirty system is causing the troubles!

Also - do you by by any chance have a heat gun - paint stripping type thing?

Replacement boiler £? A wide guesstimate, depending on a lot of things, maybe £1500 - £2500.

 

[adamtw]

Baxi/Potterton service team, they want to charge £349 inc parts, labour and VAT to fix any/all problems and give me a 1 year warranty

Bijaysus. For that I'd happily fit a new pump, diverter, pcb (it'll need one soon) and a couple of temp sensors. And they can still turn round and say it's your dirty system is causing the troubles!

Also - do you by by any chance have a heat gun - paint stripping type thing?

Surely not if I've just had the system flushed?

If only I could find a chappie like yourself nearby!

No, not got a heat gun. Why?

 

[adamtw]

DO WHAT WE SAY AND GIVE US A CHANCE OF DIAGNOSING THE FAULT

Temporarily turn off the cold water feed to the boiler. Then run the heating for 10 minutes and see if it improves.

I did this and left it for an hour to make sure, there was no difference in the heating, none of the rads got any warmer.

Strike One!

 

[Gasguru]

Prob need a new diverter. If the hex grub screws can be losened its an easy job (just replace the front end) otherwise entire diverter has to be replaced so not quite so straightforward.

 

[Agile]

I would be rather stronger that Geoff, I would say that it IS the diverter as I said some while ago!

That assumes that at some point you have unscrewed the pump nut and felt that its turning ???

Tony