Pump or Blocked Pipes?

[SteveMFF]

Hey All,

So my tenants have been having issues with the boiler for the last month or two now. I've had a heating engineer out who has tried all kinds of things but we still have no solution. I believe we have narrowed it down to either a blockage in the pipes or the pump has issues. He's tried various things for both but no joy. Obviously if it's the pipes it's a much bigger headache so I'm hoping someone here has some ideas for experiments we could try to isolate the cause before I buy a pump only to discover its the pipes or take up all my floors only to discover it was the pump!

Here's the flat details and some of the things we've tried...

- Jaguar 28KW Combi boiler (from reading on here I see buying this may have been my first mistake :biggrin5
- Small ground floor flat with boiler in the kitchen - 5 small rads and one large rad in total.
- Remote thermostat in lounge that triggers the boiler in the kitchen (seems to work fine)
- I have always had to top the boiler up a little more ofter than normal (maybe once every few weeks or once a month in the winter when it's in daily use) to keep the pressure correct so there may be a small leak somewhere but I lived there for several years and never noticed any evidence of leaks in the system or any additional issues. Still it's a possibility.

In essence the issue you see is the boiler firing up as it should and the water quickly reaches the prescribed temp but then it switches off and doesn't come back on so you get a short burst hot water to the rads but no more and they never really heat up properly. If you set different tempretures it turns off at the appropriate point (6 or 7 degrees past - so if it's set to 65 I see the boiler click off at 70ish) so I think the thermostat is OK

The first thing he changed was the plate heat exchanger as he thought this was probably scaled up and causing the issue. He also looked at the obvious culprit, the pump, but he says it seems to work OK, he then got a pressure jet to flush any blockages out of the pipes but, again, it doesn't seem to have really helped. At the moment he's left it with some balancing of the valves to try to even out the small amount of heat getting through the rads but is stumped what to try.

OK so here's the thing, I know from my fathers (oil) boiler that just because the pump seems to be working doesn't always mean that it really is. I don't know how the HE tested it but I assume he had the right tools but can anyone think of some tests that we could run on the system to isolate if the issue is pump or pipes? or perhaps there is something else we've overlooked as a cause?

I don't mind paying the ££'s to fix this but I want to be reasonably sure I know the culprit before I start ripping up floors.

Apologies if I got some of the terminology wrong, I'm learning about heating systems as I go here :biggrin5:


Thanks

 

[Howsie]

Welcome Steve.

I doubt its a problem with your pipes if it gets hot initially. You need a decent GSR engineer to diagnose your boiler problem, that's where the problem lies in my mind.

 

[chris watkins]

Hi Steve & welcome
I take it that it did work OK when you lived there ? The years of adding fresh oxygenated water to the system are likely to have now taken there toll.
You need to change heating engineers, if the one you are using can't work out what the problem is he an't no good, but I bet he is cheap!
He will cost you more in the long run just like that leak that was not found.

There are to many variable without being on site it is not possible to give you meaning full advice apart from the above.
Post your area / post code I am sure someone on here will be able to help.

 

[SteveMFF]

Welcome Steve.

I doubt its a problem with your pipes if it gets hot initially. You need a decent GSR engineer to diagnose your boiler problem, that's where the problem lies in my mind.

Just to clarify it's the boiler that seems to (quickly) get up to temp, the rads never get above luke warm. Not sure if this changes the possibility of the of the issue being in the pipes or not.

I think your right I'm just going to have to find another HE, I guess I just like learning about this stuff so I wanted to diagnose myself (don't worry, I know I can't actually do any work on the boiler but it would be good if I could learn something about heating systems from this experience)

 

[chris watkins]

You have Steve, find leaks on system & repair don't just keep topping up & use inhibitors in the system water to stop corrosion. Very important.

 

[Ollieg]

The old plate heat exchanger should of given your plumber all the info needed to make a diagnosis. Was it full of crud???

 

[SteveMFF]

The old plate heat exchanger should of given your plumber all the info needed to make a diagnosis. Was it full of crud???

Unfortunately I don't know. I wish I could give you a better answer but I let my flat through a letting agency and this was their guy so a lot of the information I've got about solutions tried has largely come through them and to say the agency is badly organised is an understatement. I wasn't even aware how much of a problem the heating had been over the winter till the letting agency told me the tenants had threatened to withold rent and then moved out.

On the plus side this does mean I've got to dump the letting agency and we can go around and take a proper look at it ourselves now which is why I was hoping there might be a few tests I could try out to isolate the fault. I'll be taking my dad, who's visiting, with me as he was a heating engineer for many years before retiring.

Also it gives us a chance to find any of these leaks. As Chris said it's better to take the short-term pain and fix than keep applying a band-aid.

Cheers

 

[SteveMFF]

Hey All,

OK so I'm arranging a HE from this site to come around and look at the system but in the meantime I did a few tests on the hot water and found something that may, or may not, be interesting in pinpointing the issue.

If I set the HW to say 60c on the boiler and run the kitchen tap (right next to the combi) the temp will gradually rise to 60, drop down a few degrees, come back up etc. Basically exactly what you would expect (and different from the rads where it gets to temp but then switches off for an extended period of time).

Here's the interesting bit though. If I set the HW to 60c and run the bathroom tap (about 15ft away) the temp never gets to 60, it'll maybe make it to 48/50 (on the boiler readout) but never get past there. The water temp then maintains in the 47-51(ish) range for as long as the tap is open.

So my Q to all you maintenance guru's out there is there an obvious culprit that would cause this anomaly in HW temps over the increased distance?

 

[Scott_D]

If you are opening the bath tap which has a higher flow rate than the kitchen tap the boiler cant heat the water as fast.
Try opening the bath tap half way and see if you get the same reading.
You will also lose some heat from un-insulated pipe over a distance

 

[SteveMFF]

If you are opening the bath tap which has a higher flow rate than the kitchen tap the boiler cant heat the water as fast.
Try opening the bath tap half way and see if you get the same reading.
You will also lose some heat from un-insulated pipe over a distance

Hi Scott,

Good point about the flow rate. I think in this instance it might not be the issue though as this is a sink tap in the showeroom (no bath, sorry for the misleading bathroom reference). I couldn't swear that there is no difference in the flow but I don't believe there is but I'll double check when I'm around there again with partially opened taps and different temp settings.

Also point taken about the inevitable drop in temp through the pipes although, in this case, it's simply the boiler readout itself I'm going off.

More experimentation then, this heating business is fun :detective:

 

[Howsie]

I doubt very much that your boiler is raising the water temperature to 60C. What is the temp coming out of the taps? You're boiler spec will tell you what its supposed to be able to do.

 

[SteveMFF]

I doubt very much that your boiler is raising the water temperature to 60C. What is the temp coming out of the taps? You're boiler spec will tell you what its supposed to be able to do.

Hey Howsie,

60c is the max the boiler will push out HW according to the specs on the inside of the cover and it's the max you can set it to. I chose this once I noticed the discrepancy as I wanted to try to get as big of a differential as I could so you could really tell if the temp running over your hand was different. Of course it's always tricky, if you are expecting something to be hotter/colder it's easy to get fooled into that even if there is no real difference. I'll take a thermometer round with me next time for science.

I know the HE will probably see the issue pretty quickly but I think it's still interesting to try to figure out in the mean time what is important and what is not. When I started this I couldn't have told you the difference between a heat exchanger and a venturi! I mean I still can't, but at least I can take the front off the boiler now so that's a start :smart:

Cheers,
Steve

 

[Howsie]

I believe the spec for that boiler is a temp rise of 30 to 35c and I doubt the incoming main temp will be 25c.