Save me some money - combi fault?

[A.Lee]

Well, after thinking the combi boiler was fixed, it has started playing up again. Alpha 240P, around 10 years old. DHW runs for 2 minutes, then cuts out for 20 seconds or so, then restarts, cuts out after a 2 minutes or so etc etc.

New DHW heat exchanger fitted, as this was pointed as the most likely cause of the fault. It did run well for 2 weeks after. Rang Alpha, who seemed to think it could now only be the Primary temp sensor failing, or the primary heat exchanger fouled up.

New sensor fitted this week. No change at all, so it looks like it is the primary heat exchanger.

The sytem had Screwfix own brand cleaner in it for a week, then flushed out. Is it worthwhile putting a good quality cleaner in it (Fernox FS3?), then flushing through again? The best way to flush through - remove both CH pipes from the bottom of the boiler, then attach hosepipes to them, and flush through like that?

Any other thing I should look at?

And if flushing through isnt the thing to cure it, is it going to be worthwhile buying a new heat exchanger, taking out the old one to clean it, or just getting a new boiler?

Thanks Alan.

[Andrew Gabriel]

I would check to see if the new DHW heat exchanger has got clogged with rust again. The timing would be about right if there's still lots of rust in the system.

[A.Lee]

Well I took it all apart again. The DHW exchanger had around 4 or 5 rust flakes in it, no more, so attention turned to the primary heat exchanger. I tried to undo its connecting pipes, but they were too tight to be undone, so plan B was to flush it through again.Radiator input tap was turned off at the boiler, leaving the output tap open, then undid the drain point at the furthest radiator, then turn on the filling loop pipe fully, pressure up to 1.5 bar on the meter, and coming out rather fast from the drain. This ran for half an hour. Put it all back together then, and had great difficulty in getting the pilot to stay alight. Thermocouple seemed to be ok, so it looked like the overheat themostat cutting off the gas, took it out, tested it for conductivity, and not a problem. Put it back with good connections, and it did stay alight eventually. Looks like the thermostat had a bad connection.

Tested, and found everything working as it should do. Great.

Now, I've got some Fernox cleaning fluid here. Would it be wise to get the whole system cleaned again this weekend?

Ta Alan.

[Doctor Drivel]

Was the flow running through the heat exchanger?

Yes.

On the CH return to the boiler fit this filter:

enough to buy.

grabs all the crud and magentite and protects the boilers heat exchangers and the rest of the system too.

You probably replaced a DHW heat exchanger for no reason. This will prevent alot of problems.

[A.Lee]

For £108, I think i'll stick with the 'thorough flush every ten years' method. For a new boiler it may act as peace of mind, but on an old one it is a poor cost/benefit ratio IMO.

Ta Alan.

[Doctor Drivel]

Then it is you that suffers the breakdowns and corrosion.

[Dave Plowman (News)]

Using inhibitor on a leak free system is the cheapest way to prevent corrosion. Filters are simply unnecessary. If they were a requirement boiler makers would fit them.

[Doctor Drivel]

Alpha fit one in the boiler. You are a plantpot knowing nothing of heating systems, so please eff off.

[dennis]

Eaga insist on having a spiravent fitted to the systems they pay for.

I googled for info but its very limited. The plumber said there was a drain on it to remove the dirt but to ignore it as it would never get dirty as long as the inhibitor wasn't drained. I wanted to find out how much they were as they are supposed to be extremely good at removing air.

[Doctor Drivel]

until the inhibitor loses is effect then corrosion starts.

[Dave Plowman (News)]

You change it before this happens. Still much cheaper than a filter. And the correct way to go about things. Prevention is always better than 'cure'.

[Doctor Drivel]

Please eff off as you are a total plantpot.