Alpha CD20S Dropping Pressure Daily

[JKBDIY]

Hello;

For several months now, our Alpha CD20s has been dropping pressure on a daily basis. When the boiler is running (either CH or DHW), pressure is fine, staying in the green range according to the gauge. Pressure only tends to drop when the thermostat is turned down - most often at night, when we'll turn it down to 15c or so before going to bed. Inevitably, I wake up to a cold house and to discover the system pressure has dropped to zero, or near zero.

I had a British Gas homecare plan, but this expired March 1st. During the month of February, I had them out 4 times and they never corrected the fault for more than a couple of days or so. I'm convinced they didn't try very hard, and they certainly didn't go so far as to replace anything expensive - no doubt because my plan was expiring and I wasn't planning to renew.

Because the pressure holds when the system is hot AND because British Gas did, at one time, fix it sufficiently that pressure held for 3-4 days (including cycling on and off a few times), I'm inclined to think the problem is with the boiler, and not a leaking system. There are no drips at rads, nor wet ceilings. The ground floor rads don't have drips but I can't say for certain what's going on under the floor as I'm loathe to tear those up before exhausting other options.

British Gas said at the time that they 'cleaned the line to the expansion vessel' (visit 1), 'drained vessel, cleaned pipe, recharged, and tested to temp' (visit 2), 'replaced isolation valve' (visit 3)(isolation valve did have a minor leak, a few drops per day), and 'tightened TRV to correct leak at radiator' (visit 4) (said radiator did have a VERY minor leak at the valve - not amounting even to a drip on the floor but just a bit of moisture at the nut).

Now, the pressure drop persists, as described above. When hot, the pressure stays steady, not launching up high which might indicate a problem with the vessel.

I'm tempted to try the old perfume in the system routine, unless it's already obvious to any readers that this is a clear fault with the expansion vessel, heat exchanger, or something else???

 

[JKBDIY]

Update: tonight I have allowed the boiler to cool for several hours, topped up to working pressure, and isolated the boiler from the rest of the system by closing both inlet and outlet valves. A couple of hours later I have checked back to find that pressure is below minimum and I see a steady drip from condensate pipe. Am I correct in suggesting that this is most likely an issue with the heat exchanger and that BG (see above) have shafted me?

 

[Harry Bloomfield]

Am I correct in suggesting that this is most likely an issue with the heat exchanger and that BG (see above) have shafted me?

Yep!

 

[gas112]

how would the guys attending know you were not going to be renewing your plan ?
Did they at anytime suggest isolating the boiler and leaving you with no heat for a day or so ?

 

[JKBDIY]

how would the guys attending know you were not going to be renewing your plan ?
Did they at anytime suggest isolating the boiler and leaving you with no heat for a day or so ?

In fairness, they wouldn't. I imagine all such maintenance plan providers look to minimise expense where possible (and inform their technicians to do the same). At no point was there a suggestion of isolating the boiler. They all tested it to temp, even after my explaining that the boiler would run all day, at pressure, just fine, but that pressure would drop after the thermostat hit temp and the boiler cycled off (or, as above, when we'd turn the thermostat down at night, cycling the boiler off). After the first visit, the expansion vessel should have been ruled out, and the leaks at the iso valve and the one radiator amounted to, at best, a thimble-full per day, not enough that I'd be topping up the boiler from 0 bar every morning.